Added foveated rendering for the Quest

- Eyes render under a VK_EXT_fragment_density_map: full rate around each eye's forward direction,
  2x2 then 4x4 pixel blocks towards the edges ([vr] foveation = off|low|medium|high, default off).
  XR_FB_foveation cannot help here: the runtime's maps only shape passes drawing into its
  swapchain, and the eyes reach it through a copy.
- aurora-main/patches/dawn/aurora_fdm.inc: Dawn enables the extension only on request and for
  dynamic rendering, flags every render pipeline, and chains an immutable RG8 map into any pass
  whose first color attachment is a view bound to one (ABI: include/aurora/dawn_fdm_abi.h).
- android/Build-QuestDawn.ps1 builds the pinned Dawn revision with those patches for arm64
  (dawn-build CI flags, protobuf off) into a cached package; Build-Quest.ps1 links it
  (-StockDawn opts out) and AuroraDawnProvider.cmake enables the ABI from its manifest.
- lib/gfx/foveation.hpp generates the maps (32 px per texel, densities 255/127/63); an eye is
  foveated only when single_pass_eyes draws it in one render pass. Menus never are.
- Live level from the headset panel's VR tab and the launcher; the launch decides whether the
  device has maps. debug.wiicompiled.foveation and debug.wiicompiled.fdm for A/B.
- Tests: Foveation cases in gx_fifo_tests, mkw_vr_config_tests. Docs: OPENXR.md, quest-port.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

aurora-main/include/aurora/aurora.h

@@ -245,6 +245,11 @@ typedef struct {
   // Enables renderer features needed by an external XR compositor. The normal
   // desktop path is unchanged when false.
   bool xrInterop;
+  // Asks for fragment density maps on the Vulkan device, for foveated eye
+  // rendering (aurora_set_stereo_foveation). Only a Dawn built with Aurora's
+  // patches has them (the Quest build). Every render pipeline is then built to
+  // run under a density map, so set it only when foveation may be used.
+  bool xrFragmentDensityMap;
   // Optional OpenXR-selected D3D adapter. Supplying the runtime's LUID before
   // device creation keeps Dawn and the compositor on the same physical GPU.
   bool hasD3D12AdapterLuid;