[Feat] (DirectGLES): implement GL_ANY_SAMPLES_PASSED occlusion queries

DirectGLES never registered BeginOcclusionQuery/EndOcclusionQuery, so
the frontend rejected the occlusion query targets entirely; the CTS
tests that use them (e.g. packed_depth_stencil.verify_partial/mixed_
attachments) left a stray GL_INVALID_ENUM that a later, unrelated
glGetError() check would report as its own failure
("Uploading buffer data failed" at gluDrawUtil.cpp:363).

Occlusion queries are core ES3 (glGenQueries/glBeginQuery(GL_ANY_
SAMPLES_PASSED, ...)/glEndQuery/glGetQueryObjectuiv), unlike the timer
queries which need GL_EXT_disjoint_timer_query, so they're wired up
unconditionally (independent of MOBILEGL_DISABLE_TIMERQUERY) using the
same handle-based GetQueryResult64/DeleteBackendQuery plumbing already
shared with timer queries. GetQueryResult64 now reads the 0/1 result
through the core 32-bit glGetQueryObjectuiv getter for occlusion
handles instead of the timer-only 64-bit GL_EXT_disjoint_timer_query
getter, since a driver can fully support core occlusion queries while
lacking that extension entirely.

MobileGL/MG_Backend/DirectGLES/DirectGLES.h

@@ -130,6 +130,11 @@ namespace MobileGL::MG_Backend::DirectGLES {
     BackendQueryHandle BeginTimeElapsedQuery();
     void EndTimeElapsedQuery(BackendQueryHandle query);
     BackendQueryHandle QueryCounterTimestamp();
+    // GL_ANY_SAMPLES_PASSED(_CONSERVATIVE) occlusion queries: core ES3, independent of
+    // GL_EXT_disjoint_timer_query and of MOBILEGL_DISABLE_TIMERQUERY. Results/deletion
+    // flow through GetQueryResult64/DeleteBackendQuery like the timer queries above.
+    BackendQueryHandle BeginOcclusionQuery();
+    void EndOcclusionQuery(BackendQueryHandle query);
     Bool IsQueryResultAvailable(BackendQueryHandle query);
     // Returns true when a final value landed in *outNanoseconds (a zero for
     // null or stale-generation handles IS final: the frontend may cache it