Auto merge of #23863 - jdm:gstreamer-uwp, r=ferjm

Various UWP GStreamer improvements

There are a number of positive changes in these commits:
* we successfully load GStreamer plugins in ARM64 UWP builds
* we correctly link the ARM64 ANGLE libraries when appropriate
* it is no longer necessary to manually set the LIB environment variable on Windows
* we automatically download and link against UWP-friendly GStreamer binaries when building with `--uwp`
* the use of vcruntime140.dll, msvcp140.dll and api-ms-win-crt-runtime-l1-1-0.dll in the UWP application has been removed and the build does not repackage them
* the set of base supporting GStreamer DLLs has been expanded to allow the gstlibav plugin to load correctly

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `___` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #23742
- [x] There are tests for these changes

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etc/taskcluster/decision_task.py

@@ -129,7 +129,6 @@ windows_build_env = {
     },
     "arm64": {
         "PKG_CONFIG_ALLOW_CROSS": "1",
-        # No GStreamer support for arm64 windows yet.
     },
     "all": {
         "PYTHON3": "%HOMEDRIVE%%HOMEPATH%\\python3\\python.exe",
@@ -377,12 +376,15 @@ def windows_arm64():
     return (
         windows_build_task("Dev build", arch="arm64", package=False)
         .with_treeherder("Windows arm64")
-        .with_script(
-            "python mach build --dev --libsimpleservo \
-              --target aarch64-pc-windows-msvc \
-              --with-raqote \
-              --without-wgl",
+        .with_file_mount(
+            "https://dist.nuget.org/win-x86-commandline/latest/nuget.exe",
+            path="nuget.exe"
         )
+        .with_script(
+            "%HOMEDRIVE%%HOMEPATH%\\nuget.exe install ANGLE.WindowsStore.Servo \
+              -Version 2.1.13 -o %HOMEDRIVE%%HOMEPATH%\\repo\\support\\hololens\\packages",
+        )
+        .with_script("python mach build --dev --uwp --win-arm64")
         .find_or_create("build.windows_arm64_dev." + CONFIG.task_id())
     )