Remove cpp_std overrides and add support for VS 2019

This MR depends on gst-plugins-good!182 (merged)

commit d20e92ff:

recipes: Don't set cpp_std anymore, it's set per-plugin
See:
https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/merge_requests/301
https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/merge_requests/182

commit 5c2f64b1:

cerbero: Add support for building with VS2019

commit aeae176a:

meson.recipe: Add support for VS2019
Bumping to 0.50.1 would also work, but it's too close to the 1.16
release to do that.

Closes #126 (closed)