Add android.opengl.EGLExt class for EGL extensions

Add the ES-relevant constants from the EGL_KHR_create_context
extension. These allow apps to check which EGLConfigs (if any) support
ES3 contexts. Otherwise, the app has to create a context with an
EGLConfig and then check whether it is an ES2 or ES3 context.

Also move eglSetPresentationTimeANDROID from EGL14 to EGLExt, since it's an
extension function. It's new in API 18.

Bug: 8678160
Change-Id: I3cba6e59ebb0a3a4c4012aa54a36b940c288bcec