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/xml/toyml.py

@@ -0,0 +1,112 @@
+#!/usr/bin/env python
+from collections import defaultdict
+import re
+import xml.etree.ElementTree as ET
+import yaml
+
+
+def etna_to_yml(xml):
+    defs = xml.find('functions')
+    functions = defaultdict(dict)
+    for f in defs.findall('function'):
+        name = f.get('name')
+        ret = f.find('return')
+        if ret is not None:
+            ret = ret.get('type')
+        if ret is None:
+            ret = 'void'
+
+        params = []
+        for p in f.findall('param'):
+            params.append('{} {}'.format(p.get('type'), p.get('name')))
+
+        functions[name] = [ret] + params
+
+    return functions
+
+
+def lua_to_yml(xml):
+    typemap = xml.find('typemap')
+    types = {}
+    for t in typemap:
+        name = t.get('typename')
+        types[name] = t.get('C-lang', name)
+
+    defs = xml.find('functions').find('function-defs')
+    functions = defaultdict(dict)
+    for f in defs.findall('function'):
+        cat = f.get('category')
+        ret = f.get('return')
+        ret = types.get(ret, ret)
+        func = f.get('name')
+
+        params = []
+        for param in f.findall('param'):
+            typ = param.get('type')
+            typ = types.get(typ, typ)
+            name = param.get('name')
+            kind = param.get('kind')
+            if kind in ('array', 'reference', 'array[size]'):
+                typ = typ.rstrip()
+                if not typ.endswith('*') or kind == 'reference':
+                    typ += ' *'
+                if not 'const' in typ and param.get('input', 'false') == 'true':
+                    typ = 'const ' + typ
+            p = '{} {}'.format(typ, name)
+            p = p.replace('* ', '*')
+            params.append(p)
+
+        args = [ret]
+        args.extend(params)
+        functions[cat][func] = args
+    return functions
+
+
+def khronos_to_yml(xml):
+    def extract(node):
+        return node.findtext('ptype') or node.text, node.findtext('name')
+
+    def clean(s):
+        return re.sub('\s+', ' ', s).strip()
+
+    defs = xml.find('commands')
+    functions = defaultdict(dict)
+    for f in defs.findall('command'):
+        proto = f.find('proto')
+        ret, name = extract(proto)
+        params = []
+        for param in f.findall('param'):
+            params.append(clean(' '.join((param.itertext()))))
+
+        functions[name] = [ret] + params
+    return functions
+
+
+def to_yml(filename):
+    with open(filename, 'r') as f:
+        data = f.read()
+
+    data = re.sub(' xmlns="[^"]+"', '', data, count=1)
+    xml = ET.fromstring(data)
+
+    if xml.tag == 'root':
+        functions = etna_to_yml(xml)
+    elif xml.tag == 'specification':
+        functions = lua_to_yml(xml)
+    elif xml.tag == 'registry':
+        functions = khronos_to_yml(xml)
+    else:
+        print 'unrecognized root tag:', xml.tag
+
+    yml = yaml.dump(dict(functions))
+    with open(filename.replace('xml', 'yml'), 'w') as o:
+        o.write(yml)
+
+if __name__ == '__main__':
+    import sys
+    if len(sys.argv) < 2:
+        print 'Usage: {} <file.xml> [file.xml...]'.format(sys.argv[0])
+        sys.exit(1)
+    
+    for name in sys.argv[1:]:
+        to_yml(name)