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/GL/glu_mangle.h

@@ -0,0 +1,86 @@
+/*
+ * Mesa 3-D graphics library
+ * Version:  3.0
+ * Copyright (C) 1995-1998  Brian Paul
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the Free
+ * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+
+#ifndef GLU_MANGLE_H
+#define GLU_MANGLE_H
+
+
+#define gluLookAt mgluLookAt
+#define gluOrtho2D mgluOrtho2D
+#define gluPerspective mgluPerspective
+#define gluPickMatrix mgluPickMatrix
+#define gluProject mgluProject
+#define gluUnProject mgluUnProject
+#define gluErrorString mgluErrorString
+#define gluScaleImage mgluScaleImage
+#define gluBuild1DMipmaps mgluBuild1DMipmaps
+#define gluBuild2DMipmaps mgluBuild2DMipmaps
+#define gluNewQuadric mgluNewQuadric
+#define gluDeleteQuadric mgluDeleteQuadric
+#define gluQuadricDrawStyle mgluQuadricDrawStyle
+#define gluQuadricOrientation mgluQuadricOrientation
+#define gluQuadricNormals mgluQuadricNormals
+#define gluQuadricTexture mgluQuadricTexture
+#define gluQuadricCallback mgluQuadricCallback
+#define gluCylinder mgluCylinder
+#define gluSphere mgluSphere
+#define gluDisk mgluDisk
+#define gluPartialDisk mgluPartialDisk
+#define gluNewNurbsRenderer mgluNewNurbsRenderer
+#define gluDeleteNurbsRenderer mgluDeleteNurbsRenderer
+#define gluLoadSamplingMatrices mgluLoadSamplingMatrices
+#define gluNurbsProperty mgluNurbsProperty
+#define gluGetNurbsProperty mgluGetNurbsProperty
+#define gluBeginCurve mgluBeginCurve
+#define gluEndCurve mgluEndCurve
+#define gluNurbsCurve mgluNurbsCurve
+#define gluBeginSurface mgluBeginSurface
+#define gluEndSurface mgluEndSurface
+#define gluNurbsSurface mgluNurbsSurface
+#define gluBeginTrim mgluBeginTrim
+#define gluEndTrim mgluEndTrim
+#define gluPwlCurve mgluPwlCurve
+#define gluNurbsCallback mgluNurbsCallback
+#define gluNewTess mgluNewTess
+#define gluDeleteTess mgluDeleteTess
+#define gluTessBeginPolygon mgluTessBeginPolygon
+#define gluTessBeginContour mgluTessBeginContour
+#define gluTessVertex mgluTessVertex
+#define gluTessEndPolygon mgluTessEndPolygon
+#define gluTessEndContour mgluTessEndContour
+#define gluTessProperty mgluTessProperty
+#define gluTessNormal mgluTessNormal
+#define gluTessCallback mgluTessCallback
+#define gluGetTessProperty mgluGetTessProperty
+#define gluBeginPolygon mgluBeginPolygon
+#define gluNextContour mgluNextContour
+#define gluEndPolygon mgluEndPolygon
+#define gluGetString mgluGetString
+#define gluBuild1DMipmapLevels mgluBuild1DMipmapLevels
+#define gluBuild2DMipmapLevels mgluBuild2DMipmapLevels
+#define gluBuild3DMipmapLevels mgluBuild3DMipmapLevels
+#define gluBuild3DMipmaps mgluBuild3DMipmaps
+#define gluCheckExtension mgluCheckExtension
+#define gluUnProject4 mgluUnProject4
+#define gluNurbsCallbackData mgluNurbsCallbackData
+#define gluNurbsCallbackDataEXT mgluNurbsCallbackDataEXT
+
+#endif