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, verify ANGLE can be selected or rejected
Change-Id: I41af7fe02ca6237db042b5f8bdfbab3c9f76078a
(cherry picked from commit a2e5faf4b23bf0b8b84ffc1d67d545e3dd4f8c63)