Enable GLES3 on Android

Add necessary build flags and switch from using a
GLES2 context to a GLES3 one.

This also enables building for OpenXR

Co-authored-by: m4gr3d <fhuyakou@gmail.com>
Co-authored-by: dsnopek <dsnopek@gmail.com>

platform/android/os_android.cpp

@@ -478,7 +478,6 @@ OS_Android::OS_Android(GodotJavaWrapper *p_godot_java, GodotIOJavaWrapper *p_god
 
 #if defined(GLES3_ENABLED)
 	gl_extensions = nullptr;
-	use_gl2 = false;
 #endif
 
 #if defined(VULKAN_ENABLED)