egl, wgl: Finish implementing available EGL functions
I believe this is everything that already exists in st, stw, Gallium, etc, which can be trivially hooked up to EGL:
- Pbuffers
- Binding surfaces as textures
- I ratholed on this a while to understand why the WGL frontend does this with a Y-flipping copy, where GLX and EGL don't. Looks like consumers of EGL/GLX are just expected to know that reading the surface will be upside down, and the NOK extension for pixmaps added a query to specifically expose that.
- Images
- Sync objects
And a few other misc things.
Lightly tested, since EGL content for Windows is rare, but after hacking up some piglit tests and finding one EGL/GLES3 sample suite, this seems to work.