[Feat] (MG_Util/SelfTest, android-plugin): driver POST self-test screen

Opening a MobileGL plugin APK now shows a POST screen that probes the
device's GLES and Vulkan drivers independently against MobileGL's
expectations - a device may satisfy only one backend - and reports a
per-backend verdict (OK / DEGRADED / UNSUPPORTED) with per-check rows.

The GLES probe builds its own ES3 pbuffer context on the system driver
and reuses FillInGLESCapabilities, including the indirect-draw
gl_InstanceID semantics probe; the Vulkan probe checks instance/device
requirements and the optional features each DirectVulkan path degrades
without. Results serialize as ASCII-safe JSON through a JNI entry in
libMobileGL.so; PostActivity renders them and caches the run per
process (single-flight, rotation-safe). PluginActivity keeps its
NoDisplay stub but the launcher entry moves to the POST screen; FCL
plugin discovery reads application meta-data and is unaffected.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitignore

@@ -23,4 +23,5 @@ MobileGL/MG*/cmake-build*
 /android-plugin/build
 /android-plugin/app/build
 /android-plugin/app/src/trace/jniLibs
+/android-plugin/local.properties
 tools/trace_replay/work/