Allow specifying ANGLE in manifest via meta-data

This CL allows the application's manifest to specify whether
to use ANGLE or native drivers for GLES via meta-data.

To enable, place the following within <application> and it
will be detected by the platform:

    <meta-data
        android:name:"com.android.angle.GLES_MODE"
        android:value:"angle" />

The manifest can also specify "native" to opt-out of
ANGLE, but native will be the default for Q release.

This method is in service of the tech preview of
ANGLE for Android. For Q release, we should move this
to the Android API.

Test: Manual, verified manifest can specify angle/native/foo
Change-Id: Iedc081a3700e05b8c391016704d0c9d623a4e76d
(cherry picked from commit e1cff35269c19020de5bf15028f0c4051ee508c5)