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).

android/gl4es-src/include/gl4eshint.h

@@ -0,0 +1,40 @@
+#ifndef _GL4ESINCLUDE_HINT_H_
+#define _GL4ESINCLUDE_HINT_H_
+
+// Custom hints to handles some specifics gl4es options
+
+// same as using LIBGL_SHRINK=x
+#define GL_SHRINK_HINT_GL4ES            0xA101
+// same as using LIBGL_ALPHAHACK=x
+#define GL_ALPHAHACK_HINT_GL4ES         0xA102
+// same as using LIBGL_RECYCLEFBO=x
+#define GL_RECYCLEFBO_HINT_GL4ES        0xA103
+// same as using LIBGL_MIPMAP=x
+#define GL_MIPMAP_HINT_GL4ES            0xA104
+// same as using LIBGL_TEXDUMP=x
+#define GL_TEXDUMP_HINT_GL4ES           0xA105
+// same as using LIBGL_COPY=x
+#define GL_COPY_HINT_GL4ES              0xA106
+// same as using LIBGL_NOLUMALPHA=x
+#define GL_NOLUMAPHA_HINT_GL4ES         0xA107
+// same as using LIBGL_BLENDHACK=x
+#define GL_BLENDHACK_HINT_GL4ES         0xA108
+// REMOVED same as using LIBGL_BATCH=x 
+#define GL_BATCH_HINT_GL4ES             0xA109
+// same as using LIBGL_NOERROR=x
+#define GL_NOERROR_HINT_GL4ES           0xA10A
+// same as using LIBGL_NODOWNSAMPLING=x
+#define GL_NODOWNSAMPLING_HINT_GL4ES	0xA10B
+// same as using LIBGL_NOVAOCACHE=x
+#define GL_NOVAOCACHE_HINT_GL4ES	    0xA10C
+// same as using LIBGL_BEGINEND=x
+#define GL_BEGINEND_HINT_GL4ES	        0xA10D
+// same as using LIBGL_AVOID16BITS=x
+#define GL_AVOID16BITS_HINT_GL4ES	    0xA10E
+// same as using LIBGL_GAMMA=xx (PANDORA only)
+#define GL_GAMMA_HINT_GL4ES             0xA10F
+
+// special value to query underlying Hardware value using glGetString
+#define GL_VENDOR_GL4ES                 (GL_VENDOR | 0x10000)
+#define GL_EXTENSIONS_GL4ES             (GL_ENXTENSIONS | 0x10000)
+#endif // _GL4ESINCLUDE_HINT_H_