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>

android/app/src/main/res/values/strings.xml

@@ -543,6 +543,12 @@
     <string name="vr_performance_level_sustained_low">Sustained low</string>
     <string name="vr_performance_level_power_savings">Power savings</string>
     <string name="vr_performance_level_default">Headset default</string>
+    <string name="vr_foveation">Foveated rendering</string>
+    <string name="vr_foveation_helper">Shades the edges of the race view in coarser blocks, where the lenses blur the picture anyway, to free GPU time for a higher render scale or a steadier frame rate. Higher levels start closer to the centre; High also coarsens the corners of the HUD. Menus are never foveated.</string>
+    <string name="vr_foveation_off">Off</string>
+    <string name="vr_foveation_low">Low</string>
+    <string name="vr_foveation_medium">Medium</string>
+    <string name="vr_foveation_high">High</string>
     <string name="vr_interpolation">VR frame interpolation</string>
     <string name="vr_interpolation_helper">Experimental. Renders extra frames between game frames at the headset\'s rate. Needs GPU headroom and adds one game frame of latency.</string>
     <string name="vr_interpolation_off">Off</string>