Updated bgfx, bx and bimg to current upstream versions. (#11493)

* Reverted "macOS, iOS: Removed OpenGL/OpenGLES support. (commit 4693983).
* Reverted "Fix macOS build" (commit ce2c2c1).
* Reverted "macOS: Fixed deprecated warnings." (commit 10a8cb6).
* Added bgfx/README.mame explaining deviations from upstream.

Author: belegdol

3rdparty/bgfx/.github/workflows/main.yml

@@ -211,10 +211,7 @@ jobs:
       fail-fast: true
       matrix:
         include: [
-          { platform: arm    },
           { platform: arm64  },
-          { platform: x86    },
-          { platform: x86_64 },
         ]
     name: android-${{ matrix.platform }}
     runs-on: ubuntu-22.04