native_render: HiDPI glyph pages, sharp UI upscaling, 4x MSAA

- CGraphicFontTexture rasterises glyph pages at the swapchain density
  (UISetFontOversample, MT_FONT_OVERSAMPLE) with anti-aliased coverage;
  metrics, packing and UVs stay the 40250 1x values. Default 1 keeps the
  verbatim bilevel path (Godot unchanged).
- native.frag: sharp-bilinear sampling for magnified UI textures.
- Multisampled colour/depth with a resolve into the swapchain (MT_MSAA,
  default 4); stats line reports msaa=N.

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

extension/src/platform/EterLib/UIRenderCommands.h

@@ -72,3 +72,10 @@ void UIRenderAdd(UIRenderCommand command);
 const std::vector<UIRenderCommand>& UIRenderCommands();
 void UIRenderSetClip(float x, float y, float width, float height);
 void UIRenderRestoreClip();
+
+// HiDPI text: CGraphicFontTexture rasterises its glyph pages at this multiple of the logical font
+// size (the swapchain's pixels per UI pixel) while keeping the 40250 glyph metrics and page UVs in
+// logical pixels. 1 (the default) is the verbatim 40250 path. Latched when the first font page is
+// created, so set it before the game creates fonts.
+void UISetFontOversample(int scale);
+int UIFontOversample();