Auto merge of #23696 - servo:hl, r=jdm

Add UWP port - bis

This is #23658 with some fixes:
- removed nspr from DLL dependencies (was breaking VS build)
- exclude symbols from header file (was breaking VS build)
- rebased

Before merging:
- please check the rebased commit that introduces the `--uwp` option (things moved around since 7c85dc09b5)
- should we wait until the WR fix lands upstream?

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ports/libmlservo/Cargo.toml

@@ -15,6 +15,7 @@ bench = false
 [features]
 canvas2d-azure = ["simpleservo/canvas2d-azure"]
 canvas2d-raqote = ["simpleservo/canvas2d-raqote"]
+egl = ["simpleservo/egl"]
 
 [dependencies]
 libservo = { path = "../../components/servo", features = ["no_static_freetype"] }