Add a new GpuService API to query persist.graphics.egl

To solve b/408439360 and b/409589250, we need to query
persist.graphics.egl in GraphicsEnvironment.java. This change
adds the GpuService API to read persist.graphics.egl value
through aidl. This way we don't need to alter the sepolicy
to expose read access of graphics_config_writable_prop to
general apps, and we can control when the persist.graphics.egl
is accessed by adding UID permission.

Flag: com.android.graphics.graphicsenv.flags.query_persist_graphics_egl
Bug: b/408439360
Bug: b/409589250
Test: make, flash to shiba, check there is no avc:  denied  { read } for  name="u:object_r:graphics_config_writable_prop
Change-Id: Ic12c6a3ca515728740f6e9c70bb3834d67d3231e