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/spec/yml/glext-1.1.yml

@@ -0,0 +1,36 @@
+#GLES 1.1 Extensions (might be GLES 2.0 Core)
+glBlendColor_OES_: [void, GLclampf red, GLclampf green, GLclampf blue, GLclampf alpha]
+glBlendEquation_OES_: [void, GLenum mode]
+glBlendEquationSeparate_OES_: [void, GLenum modeRGB, GLenum modeA]
+glBlendFuncSeparate_OES_: [void, GLenum sfactorRGB, GLenum dfactorRGB, GLenum sfactorAlpha, GLenum dfactorAlpha]
+# glTexGenfOES_OES_: [void, GLenum coord, GLenum pname, GLfloat param]
+glTexGenfv_OES_: [void, GLenum coord, GLenum pname, "const GLfloat *params"]
+glTexGeni_OES_: [void, GLenum coord, GLenum pname, GLint param]
+# glTexGenivOES_OES_: [void, GLenum coord, GLenum pname, "const GLint *params"]
+
+glGenFramebuffers_OES_: [void, GLsizei n, "GLuint *ids"]
+glDeleteFramebuffers_OES_: [void, GLsizei n, "GLuint *framebuffers"]
+glIsFramebuffer_OES_: [GLboolean, GLuint framebuffer]
+glCheckFramebufferStatus_OES_: [GLenum, GLenum target]
+glBindFramebuffer_OES_: [void, GLenum target, GLuint framebuffer]
+glFramebufferTexture2D_OES_: [void, GLenum target, GLenum attachment, GLenum textarget, GLuint texture, GLint level]
+glGenRenderbuffers_OES_: [void, GLsizei n, "GLuint *renderbuffers"]
+glFramebufferRenderbuffer_OES_: [void, GLenum target, GLenum attachment, GLenum renderbuffertarget, GLuint renderbuffer]
+glDeleteRenderbuffers_OES_: [void, GLsizei n, "GLuint *renderbuffers"]
+glRenderbufferStorage_OES_: [void, GLenum target, GLenum internalformat, GLsizei width, GLsizei height]
+glBindRenderbuffer_OES_: [void, GLenum target, GLuint renderbuffer]
+glIsRenderbuffer_OES_: [GLboolean, GLuint renderbuffer]
+glGenerateMipmap_OES_: [void, GLenum target]
+glGetFramebufferAttachmentParameteriv_OES_: [void, GLenum target, GLenum attachment, GLenum pname, "GLint *params"]
+glGetRenderbufferParameteriv_OES_: [void, GLenum target, GLenum pname, "GLint * params"]
+
+glDrawTexi_OES_: [void, GLint x, GLint y, GLint z, GLint width, GLint height]
+glDrawTexf_OES_: [void, GLfloat x, GLfloat y, GLfloat z, GLfloat width, GLfloat height]
+
+glMultiDrawArrays_OES_: [void, GLenum mode, "const GLint *first", "const GLsizei *count", GLsizei primcount]
+glMultiDrawElements_OES_: [void, GLenum mode, "GLsizei *count", GLenum type, "const void * const *indices", GLsizei primcount]
+
+glGetProgramBinary_OES_ : [void, GLuint program, GLsizei bufSize, "GLsizei *length", "GLenum *binaryFormat", "GLvoid *binary"]
+glProgramBinary_OES_ : [void, GLuint program, GLenum binaryFormat, "const GLvoid *binary", GLint length]
+
+glDrawBuffers_EXT_ : [void, GLsizei n, "const GLenum *bufs"]