Use ANGLEGetDisplayPlatform for ANGLE determination

ANGLEGetDisplayPlatform is used to initialize various ANGLE related
system features. Use that to determine if loaded library is ANGLE or
not. This function is used elsewhere in the EGL loader. If it changes
it will be easier to catch all the dependencies if we use the same name.

Test: atest CtsAngleIntegrationHostTestCases
Bug: b/154237217
Change-Id: Ibc579604820ff1118f4dc703f0805df36359ba70