Add OpenGL ES 3 support to LWJGL3 ANGLE backend

Description

The gdx-lwjgl3-angle backend currently only exposes ANGLE_GLES20.

When ANGLE support was added in libGDX 1.11.0, GLES 3 was not supported because ANGLE's Metal backend only supported GLES 2 at the time.

ANGLE now lists OpenGL ES 3.0 support over Metal as complete: https://github.com/google/angle#level-of-opengl-es-support-via-backing-renderers

Would it be possible to add GLES 3 support to the libGDX ANGLE backend, e.g. via an ANGLE_GLES30 mode exposing Gdx.gl30?

This would make ANGLE/Metal a viable alternative on macOS for applications that require GLES 3 features.