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/tests/test.sh

@@ -0,0 +1,41 @@
+#!/bin/bash
+#
+# WARNING: do not execute this file unless you are aware of what you're doing.
+# This file is meant to be executed by ctest.
+
+export LIBGL_FB=3
+export LIBGL_SILENTSTUB=1
+export LIBGL_NOBANNER=1
+export LIBGL_NOERROR=1
+
+tar xf ../traces/$1.tgz
+apitrace dump-images --calls="$2" $1.trace >/dev/null
+exit_status=$?
+test $exit_status -ne 0 && echo "Test returned a non-zero status $exit_status (segmentation fault?)"
+rm $1.trace
+
+if [[ -f $1.$2.png ]]
+then
+	mv $1.$2.png $1.$2.$LIBGL_ES.png
+
+	EXTRACT=""
+	if [[ ! -z "$4" ]]
+	then
+		EXTRACT="-extract $4"
+	fi
+	result=$(compare -metric AE -fuzz 20% $EXTRACT ../refs/$1.$2.png $1.$2.$LIBGL_ES.png diff_$1_GLES$LIBGL_ES.png 2>&1)
+
+	if [[ ! "$result" -lt "$3" ]]
+	then
+		echo -n "$result pixels of difference"
+		exit 1
+	fi
+
+	[[ -e diff_$1_GLES$LIBGL_ES.png ]] && rm diff_$1_GLES$LIBGL_ES.png
+	[[ -e $1.$2.$LIBGL_ES.png ]] && rm $1.$2.$LIBGL_ES.png
+else
+	echo -n "Failed to get snapshot"
+	exit 1
+fi
+
+exit 0