RFC: glupload: Play pipeline and wait for `sync-done` before currenting GL context

On certain GL drivers on Windows (e.g. those for Intel Arc) we see that creation of a shared context based on our wrapped WGL context (from glutin) fails with ERROR_BUSY:

0:00:00.509113900 29460 000001E07A782CC0 DEBUG              glcontext gstglcontext.c:1227:gst_gl_context_create_thread:<glcontextwgl0> Creating thread
0:00:00.509352100 29460 000001E07A782CC0 FIXME              glcontext gstglcontext.c:2041:gst_gl_wrapped_context_get_config:<glwrappedcontext0> wrapped context could not retrieve config. The application may be missing a call to gst_gl_context_fill_info() or the specific platform implemention is not implemented for retrieving the config from a wrapped OpenGL context.
0:00:00.543157300 29460 000001E07A782CC0 INFO               glcontext gstglcontext_wgl.c:402:gst_gl_context_wgl_choose_format:<glcontextwgl0> chosen config gst-gl-context-config, platform=(GstGLPlatform)GST_GL_PLATFORM_WGL, red-size=(int)8, blue-size=(int)8, green-size=(int)8, alpha-size=(int)8, depth-size=(int)24, stencil-size=(int)8, native-visual-id=(uint)5, surface-type=(GstGLConfigSurfaceType)GST_GL_CONFIG_SURFACE_TYPE_WINDOW;
0:00:00.543770000 29460 000001E07A782CC0 INFO               glcontext gstglcontext.c:1322:gst_gl_context_create_thread:<glcontextwgl0> Attempting to create opengl context. user chosen api(s) (any), compiled api support (opengl opengl3) display api (any)
0:00:00.553201100 29460 000001E07A782CC0 DEBUG              glcontext gstglcontext_wgl.c:186:gst_gl_context_wgl_create_context: gl context created: 65537
0:00:00.613589500 29460 000001E07A782CC0 DEBUG              glcontext gstglcontext_wgl.c:214:gst_gl_context_wgl_create_context:<glcontextwgl0> Available WGL extensions WGL_EXT_depth_float WGL_ARB_buffer_region WGL_ARB_extensions_string WGL_ARB_make_current_read WGL_ARB_pixel_format WGL_ARB_pbuffer WGL_EXT_extensions_string WGL_EXT_swap_control WGL_ARB_multisample WGL_ARB_pixel_format_float WGL_ARB_framebuffer_sRGB WGL_ARB_create_context WGL_ARB_create_context_profile WGL_EXT_pixel_format_packed_float WGL_EXT_create_context_es_profile WGL_EXT_create_context_es2_profile WGL_NV_DX_interop WGL_NV_DX_interop2 WGL_ARB_robustness_application_isolation WGL_ARB_robustness_share_group_isolation WGL_ARB_create_context_robustness WGL_ARB_context_flush_control
0:00:00.614036500 29460 000001E07A782CC0 DEBUG              glcontext gstglcontext_wgl.c:235:gst_gl_context_wgl_create_context:<glcontextwgl0> trying to create a GL 4.5 context
0:00:00.631649700 29460 000001E07A782CC0 DEBUG              glcontext gstglcontext_wgl.c:235:gst_gl_context_wgl_create_context:<glcontextwgl0> trying to create a GL 4.4 context
0:00:00.650484600 29460 000001E07A782CC0 DEBUG              glcontext gstglcontext_wgl.c:235:gst_gl_context_wgl_create_context:<glcontextwgl0> trying to create a GL 4.3 context
0:00:00.669332300 29460 000001E07A782CC0 DEBUG              glcontext gstglcontext_wgl.c:235:gst_gl_context_wgl_create_context:<glcontextwgl0> trying to create a GL 4.2 context
0:00:00.687633700 29460 000001E07A782CC0 DEBUG              glcontext gstglcontext_wgl.c:235:gst_gl_context_wgl_create_context:<glcontextwgl0> trying to create a GL 4.1 context
0:00:00.706444500 29460 000001E07A782CC0 DEBUG              glcontext gstglcontext_wgl.c:235:gst_gl_context_wgl_create_context:<glcontextwgl0> trying to create a GL 4.0 context
0:00:00.725763400 29460 000001E07A782CC0 DEBUG              glcontext gstglcontext_wgl.c:235:gst_gl_context_wgl_create_context:<glcontextwgl0> trying to create a GL 3.3 context
0:00:00.745413200 29460 000001E07A782CC0 DEBUG              glcontext gstglcontext_wgl.c:235:gst_gl_context_wgl_create_context:<glcontextwgl0> trying to create a GL 3.2 context
0:00:00.781065300 29460 000001E07A782CC0 WARN               glcontext gstglcontext.c:1326:gst_gl_context_create_thread:<glcontextwgl0> Failed to create context
0:00:00.781358600 29460 000001E076862100 INFO               glcontext gstglcontext.c:1079:gst_gl_context_create:<glcontextwgl0> gl thread created
0:00:00.781584200 29460 000001E076862100 DEBUG              glcontext gstglcontext.c:746:gst_gl_context_finalize:<glcontextwgl0> End of finalize
0:00:00.781787700 29460 000001E076862100 WARN            glbasefilter gstglbasefilter.c:608:gst_gl_base_filter_find_gl_context_unlocked:<gluploadelement0> error: failed to share contexts through wglShareLists 0xaa
0:00:00.782145700 29460 000001E076862100 INFO               glcontext gstglcontext.c:349:gst_gl_context_new: creating a context for display <gldisplay0>, user choice:(null)
0:00:00.782381300 29460 000001E076862100 DEBUG              glcontext gstglcontext.c:383:gst_gl_context_new:<glcontextwgl1> Done creating context for display <gldisplay0> (user_choice:(null))
0:00:00.782632900 29460 000001E076862100 DEBUG              glcontext gstglcontext.c:1058:gst_gl_context_create:<glcontextwgl1>  other_context:<glwrappedcontext0>
0:00:00.782921300 29460 000001E076862100 INFO                glwindow gstglwindow.c:295:gst_gl_window_new: creating a window, user choice:(null)
0:00:00.783246300 29460 000001E076862100 DEBUG              glcontext gstglcontext.c:956:gst_gl_context_set_window:<glcontextwgl1> window:<glwindowwin32-1>
0:00:00.783815200 29460 000001E07A782D00 DEBUG              glcontext gstglcontext.c:1227:gst_gl_context_create_thread:<glcontextwgl1> Creating thread
0:00:00.784130000 29460 000001E07A782D00 FIXME              glcontext gstglcontext.c:2041:gst_gl_wrapped_context_get_config:<glwrappedcontext0> wrapped context could not retrieve config. The application may be missing a call to gst_gl_context_fill_info() or the specific platform implemention is not implemented for retrieving the config from a wrapped OpenGL context.
thread 'main' panicked at examples\src\bin\..\glupload.rs:755:44:
called `Result::unwrap()` on an `Err` value: Received error from /GstPipeline:pipeline0/GstGLSinkBin:glsinkbin0/GstGLUploadElement:gluploadelement0: failed to share contexts through wglShareLists 0xaa (debug: Some("../gst-libs/gst/gl/gstglbasefilter.c(608): gst_gl_base_filter_find_gl_context_unlocked (): /GstPipeline:pipeline0/GstGLSinkBin:glsinkbin0/GstGLUploadElement:gluploadelement0"))

This happens because the context is made "current" inside the winit loop before asynchronous GL initialization inside GStreamer commences. As we have a Surface on the glutin side, we're not uncurrenting it anymore, and instead want to perform GStreamer pipeline initalization via that thread up-front.

One of the ways I've "found to do that" is to set the pipeline to Playing already and wait for the async-done message, at which point a shared WGL context has been created and we're able to safely make the GL context current.

In theory, since GLContext tracks whether it's current and on which thread, the upsteam source should emit an error of sorts when wglShareLists() is called on a thread where this other_context in gst_gl_context_create(_thread) was not yet current, to not make such mistakes go unnoticed as most drivers (i.e. AMD's) seem to not make an issue out of it.

For the avid reader, there's a FIXME stating that we didn't yet call fill_info() on our wrapped context; but we can't until we've made it current, which would break wglShareLists() (unless we uncurrent it). Maybe this requires a different solution after all to make this possible?