Refactor ANGLE usage code.

Previously when ANGLE is the default system driver, the ro.hardware.egl
points to ANGLE. This is fine if ANGLE is the only system drvier.
However, we would like to make ANGLE coexist with the native GLES
drivers and allow a global switch. Hence this patch refactors the
majority of the ANGLE selection logic. Loading ANGLE in the form of an
apk as well as using ANGLE as a game mode intervention should remain
functional.

Bug: b/270994705
Test: atest CtsAngleIntegrationHostTestCases
Change-Id: I31a6a5dda04a1ffaeed101e58368ad4b4ad0d54e