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>

runtime/tests/vr_config_tests.cpp

@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+#include "runtime_config.h"
+#include <cstdlib>
+#include <sstream>
+#include <string>
+#include <string_view>
+
+static void Require(bool condition) {
+    if (!condition) std::abort();
+}
+
+static RuntimeUserConfig Parse(const std::string& text) {
+    std::istringstream input(text);
+    return RuntimeConfigFile::ParseConfig(input);
+}
+
+int main() {
+    // [vr] foveation: the Quest's foveated rendering level, index-matched to
+    // aurora_set_stereo_foveation.
+    for (std::string_view level : RuntimeConfigFile::kVrFoveationLevels) {
+        Require(Parse("[vr]\nfoveation = \"" + std::string(level) + "\"\n").vrFoveation == std::string(level));
+    }
+    Require(!Parse("[vr]\nfoveation = \"ultra\"\n").vrFoveation.has_value());
+    Require(!Parse("[vr]\nfoveation = 2\n").vrFoveation.has_value());
+    Require(!Parse("[vr]\n").vrFoveation.has_value());
+    Require(std::string_view(RuntimeConfigFile::kVrFoveationDefault) == "off");
+    Require(RuntimeConfigFile::VrFoveationLevelIndex("off") == 0);
+    Require(RuntimeConfigFile::VrFoveationLevelIndex("low") == 1);
+    Require(RuntimeConfigFile::VrFoveationLevelIndex("medium") == 2);
+    Require(RuntimeConfigFile::VrFoveationLevelIndex("high") == 3);
+    Require(RuntimeConfigFile::VrFoveationLevelIndex("ultra") == 0);
+
+    // [vr] single_pass_eyes: each eye replayed in one render pass.
+    Require(Parse("[vr]\nsingle_pass_eyes = true\n").vrSinglePassEyes == true);
+    Require(Parse("[vr]\nsingle_pass_eyes = false\n").vrSinglePassEyes == false);
+    Require(!Parse("[vr]\n").vrSinglePassEyes.has_value());
+    return 0;
+}