Add ANGLE support to getDisplay

If ANGLE is enabled for this application construct the necessary
attributes to configure ANGLE and call ANGLE's eglGetPlatformDisplay
to initialize.

Test: manual - enable ANGLE for app and verify
Bug: 80239516
Change-Id: I9bbd40c660cd3bed72989fb4529e50eb608d71ea
diff --git a/opengl/libs/EGL/egldefs.h b/opengl/libs/EGL/egldefs.h
index 2600eb0..4990af6 100644
--- a/opengl/libs/EGL/egldefs.h
+++ b/opengl/libs/EGL/egldefs.h
@@ -49,6 +49,7 @@
     void*               libGles2;
 
     bool                useAngle;
+    EGLint              angleBackend;
     void*               vendorEGL;
 };