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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---
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components/servo/lib.rs

@@ -127,7 +127,8 @@ pub use servo_url as url;
 
 #[cfg(any(
     all(target_os = "android", target_arch = "arm"),
-    target_arch = "x86_64"
+    target_arch = "x86_64",
+    all(target_os = "windows", target_arch = "aarch64"),
 ))]
 mod media_platform {
     use super::ServoMedia;
@@ -135,8 +136,15 @@ mod media_platform {
 
     #[cfg(windows)]
     pub fn init() {
-        let mut plugin_dir = std::env::current_exe().unwrap();
-        plugin_dir.pop();
+        // UWP apps have the working directory set appropriately. Win32 apps
+        // do not and need some assistance finding the DLLs.
+        let plugin_dir = if cfg!(feature = "uwp") {
+            std::path::PathBuf::new()
+        } else {
+            let mut plugin_dir = std::env::current_exe().unwrap();
+            plugin_dir.pop();
+            plugin_dir
+        };
 
         let uwp_plugins = [
             "gstapp.dll",
@@ -201,7 +209,8 @@ mod media_platform {
 
 #[cfg(not(any(
     all(target_os = "android", target_arch = "arm"),
-    target_arch = "x86_64"
+    target_arch = "x86_64",
+    all(target_os = "windows", target_arch = "aarch64"),
 )))]
 mod media_platform {
     use super::ServoMedia;