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/template/base/wrap.h.j2

@@ -0,0 +1,65 @@
+{% extends "base/header.j2" %}
+{% block content %}
+
+typedef struct {
+    int format;
+    void *func;
+    void *args;
+} packed_call_t;
+
+typedef struct {
+    int func;
+    void *args;
+} indexed_call_t;
+
+enum FORMAT {
+{% for f in formats %}
+    FORMAT_{{ f.types }},
+{% endfor %}
+};
+
+{% for f in formats %}
+typedef {{ f.return }} (*FUNC_{{ f.types }})({{ f.args|args }});
+{% if f.args %}
+typedef struct {
+    {% for arg in f.args %}
+    {{ arg.type|unconst }} a{{ loop.index }}{% if arg.type == 'GLdouble' %} __attribute__ ((aligned(8))){% endif %};
+    {% endfor %}
+} ARGS_{{ f.types }};
+{% endif %}
+typedef struct {
+    int format;
+    FUNC_{{ f.types }} func;
+    {% if f.args %}
+    ARGS_{{ f.types }} args;
+    {% endif %}
+} PACKED_{{ f.types }};
+typedef struct {
+    int func;
+    {% if f.args %}
+    ARGS_{{ f.types }} args;
+    {% endif %}
+} INDEXED_{{ f.types }};
+{% endfor %}
+
+extern void glPushCall(void *data);
+void glPackedCall(const packed_call_t *packed);
+void glIndexedCall(const indexed_call_t *packed, void *ret_v);
+packed_call_t* glCopyPackedCall(const packed_call_t *packed);
+
+{% for func in functions %}
+#define {{ func.name }}_INDEX {{ loop.index }}
+#define {{ func.name }}_RETURN {{ func.return }}
+#define {{ func.name }}_ARG_NAMES {{ func.args|args(0) }}
+#define {{ func.name }}_ARG_EXPAND {{ func.args|args }}
+#define {{ func.name }}_PACKED PACKED_{{ func.types }}
+#define {{ func.name }}_INDEXED INDEXED_{{ func.types }}
+#define {{ func.name }}_FORMAT FORMAT_{{ func.types }}
+{% endfor %}
+
+{% for func in functions %}
+{{ func.return }} APIENTRY_GL4ES gl4es_{{ func.name }}({{ func.name }}_ARG_EXPAND);
+typedef {{ func.return }} (* APIENTRY_GLES {{ func.name }}_PTR)({{ func.name }}_ARG_EXPAND);
+{% endfor %}
+
+{% endblock %}