Add controller input and a laser-pointer-driven menu quad

- xr_input.c/h: an OpenXR action set (aim pose, trigger/select click, a
  menu-toggle button) plus ray/quad hit-testing, and a visible
  laser-pointer line drawn from the controller toward the hit point.
- xr_menu.c/h + MenuOverlay.java: a second composition-layer quad,
  toggled by a controller button, showing an off-screen, never-attached
  Android View tree (one "Keyboard" button so far) driven by synthetic
  touch events computed from the laser ray's hit UV.
- Migrate gl4es from a prebuilt binary baked into the Docker build-image
  to a vendored source snapshot (android/gl4es-src/) compiled from
  source at APK build time via CMake add_subdirectory(), patched through
  a new android/gl4es-patches/ (mirrors the existing engine-patches/
  pattern). This was needed to track down and fix a bug hit while
  building the menu: gl4es's fixed-pipeline emulation (fpe.c) was
  unconditionally substituting its own shader onto the menu's draw call
  (fpe_ReleventState() always sets alphafunc to a nonzero sentinel, so
  its fpe_IsEmpty() check could never see the state as empty), making
  the menu quad show the game's own rendering instead of its own
  content. Fixed by routing the menu's blit through a real
  glBlitFramebuffer() call instead of a shader-based draw, which gl4es's
  fpe.c has nothing to intercept - documented in README.md's new
  "Debugging notes" section.
- Renumber android/engine-patches/ to close the gap left by removing an
  unrelated diagnostic-only patch, and strip investigation-journal
  comments and dead diagnostic code (temporary tracing, env-var probes)
  left over from finding the bug above.
- Restructure README.md into numbered sections, document every
  engine/gl4es patch, add Android Studio dev/testing-cycle instructions,
  and generalize Quest-specific wording to any OpenXR headset. Update
  NOTICE.txt to match (gl4es is now vendored/patched source, not a
  prebuilt binary; add the OpenXR-SDK loader).

build-image/prepare-android-project.sh

@@ -1,11 +1,17 @@
 #!/usr/bin/env bash
 # Prepares android/ to be built: a scratch, patched copy of engine/ (see
-# android/engine-patches/ - engine/ itself is never modified), the
-# Android SDL2/SDL2_mixer/fluidsynth-lite/gl4es/openxr prebuilts staged
-# into jniLibs, bundled assets, and android/engine.properties (engineDir/
-# prebuiltDir, read by android/app/build.gradle). Always run inside this
-# image (via ../run-image.sh, or directly if already inside it) - it
-# reads from /opt/prebuilt/android/*, which only exists there.
+# android/engine-patches/) and of android/gl4es-src/ (see
+# android/gl4es-patches/) - neither vendored tree itself is ever modified -
+# the Android SDL2/SDL2_mixer/fluidsynth-lite/openxr prebuilts staged into
+# jniLibs, bundled assets, and android/engine.properties (engineDir/
+# gl4esDir/prebuiltDir, read by android/app/build.gradle). gl4es itself is
+# NOT prebuilt here - it's compiled from this scratch copy as a CMake
+# subdirectory of the engine's own native build (see
+# android/engine-patches/02-android-opengl-es.patch), so gl4es-patches/
+# changes only need a normal rebuild, not a build-image rebuild. Always
+# run inside this image (via ../run-image.sh, or directly if already
+# inside it) - it reads from /opt/prebuilt/android/*, which only exists
+# there.
 #
 # Two modes:
 #   (no args)      - for build-apk.sh's own gradlew, invoked in this same
@@ -30,6 +36,7 @@ fi
 REPO_ROOT="$(pwd)"
 ANDROID_DIR="$REPO_ROOT/android"
 SCRATCH_ENGINE="$REPO_ROOT/build/android-engine"
+SCRATCH_GL4ES="$REPO_ROOT/build/android-gl4es"
 PREBUILT_EXPORT_DIR="$REPO_ROOT/build/android-prebuilt"
 
 echo "== Preparing a scratch, patched copy of engine/ =="
@@ -40,6 +47,13 @@ for p in "$ANDROID_DIR"/engine-patches/*.patch; do
     patch -p1 -d "$SCRATCH_ENGINE" < "$p"
 done
 
+echo "== Preparing a scratch, patched copy of android/gl4es-src/ =="
+rm -rf "$SCRATCH_GL4ES"
+cp -a "$ANDROID_DIR/gl4es-src" "$SCRATCH_GL4ES"
+for p in "$ANDROID_DIR"/gl4es-patches/*.patch; do
+    patch -p1 -d "$SCRATCH_GL4ES" < "$p"
+done
+
 echo "== Wiring up prebuilt Android SDL2_mixer/fluidsynth-lite (BUNDLED mode, like the desktop build) =="
 mkdir -p "$SCRATCH_ENGINE/build_ext/built_sdl_mixer" "$SCRATCH_ENGINE/build_ext/fluidsynth-lite"
 cp -a /opt/prebuilt/android/sdl2_mixer/. "$SCRATCH_ENGINE/build_ext/built_sdl_mixer/"
@@ -49,18 +63,21 @@ cp -a /opt/prebuilt/android/fluidsynth-lite/include/. "$SCRATCH_ENGINE/build_ext
 
 if [ "$HOST_PATHS" -eq 1 ]; then
     : "${HOST_REPO_ROOT:?--host-paths needs HOST_REPO_ROOT set - run via ./run-image.sh, not directly}"
-    echo "== Exporting prebuilt Android SDL2/SDL2_mixer/fluidsynth-lite/gl4es for host-side use =="
+    echo "== Exporting prebuilt Android SDL2/SDL2_mixer/fluidsynth-lite/openxr for host-side use =="
     rm -rf "$PREBUILT_EXPORT_DIR"
     cp -a /opt/prebuilt/android "$PREBUILT_EXPORT_DIR"
     ENGINE_DIR_PROP="$HOST_REPO_ROOT/build/android-engine"
+    GL4ES_DIR_PROP="$HOST_REPO_ROOT/build/android-gl4es"
     PREBUILT_DIR_PROP="$HOST_REPO_ROOT/build/android-prebuilt"
 else
     ENGINE_DIR_PROP="$SCRATCH_ENGINE"
+    GL4ES_DIR_PROP="$SCRATCH_GL4ES"
     PREBUILT_DIR_PROP="/opt/prebuilt/android"
 fi
 
 {
     echo "engineDir=$ENGINE_DIR_PROP"
+    echo "gl4esDir=$GL4ES_DIR_PROP"
     echo "prebuiltDir=$PREBUILT_DIR_PROP"
 } > "$ANDROID_DIR/engine.properties"
 
@@ -75,16 +92,22 @@ cp -a "$ANDROID_DIR/gles-shaders/." "$ASSETS_DIR/shaders/"
 cp "/opt/prebuilt/soundfont/default.sf2" "$ASSETS_DIR/res/soundfont.sf2"
 cp "$REPO_ROOT/res/assets/GET_ASSETS_QUEST.txt" "$ASSETS_DIR/GET_ASSETS_QUEST.txt"
 
-echo "== Staging prebuilt Android SDL2/SDL2_mixer/fluidsynth-lite/gl4es/openxr .so's into jniLibs =="
+echo "== Staging prebuilt Android SDL2/SDL2_mixer/fluidsynth-lite/openxr .so's into jniLibs =="
+# gl4es is deliberately absent here - it's no longer prebuilt, it's compiled
+# from $SCRATCH_GL4ES as part of the engine's own native build (see
+# android/engine-patches/02-android-opengl-es.patch); AGP's own native-build
+# packaging picks up its compiled libGL.so directly, without needing it
+# staged into jniLibs by this script.
 JNI_LIBS_DIR="$ANDROID_DIR/app/src/main/jniLibs/arm64-v8a"
 rm -rf "$ANDROID_DIR/app/src/main/jniLibs"
 mkdir -p "$JNI_LIBS_DIR"
 find /opt/prebuilt/android/sdl2/lib /opt/prebuilt/android/sdl2_mixer/lib /opt/prebuilt/android/fluidsynth-lite/lib \
-    /opt/prebuilt/android/gl4es/lib /opt/prebuilt/android/openxr/lib \
+    /opt/prebuilt/android/openxr/lib \
     -name '*.so' -exec cp -a {} "$JNI_LIBS_DIR/" \;
 
 echo "== Done =="
 echo "engineDir=$ENGINE_DIR_PROP"
+echo "gl4esDir=$GL4ES_DIR_PROP"
 echo "prebuiltDir=$PREBUILT_DIR_PROP"
 if [ "$HOST_PATHS" -eq 1 ]; then
     echo "android/ is ready to open and build natively in Android Studio on the host."