Change file paths to URIs to fix "Could not run configuration in engine" on Windows (#22507)

* Change file paths to URIs to fix "Could not run configuration in engine" on Windows

Plus unskip test that was failing due to this.

Fixes #21348.

* Remove unused import

packages/flutter_tools/lib/src/vmservice.dart

diff --git a/packages/flutter_tools/lib/src/vmservice.dart b/packages/flutter_tools/lib/src/vmservice.dart
index ae7652e..0fa50cb 100644
--- a/packages/flutter_tools/lib/src/vmservice.dart
+++ b/packages/flutter_tools/lib/src/vmservice.dart
@@ -921,13 +921,12 @@
                                Uri main,
                                Uri packages,
                                Uri assetsDirectory) {
-    // TODO(goderbauer): Transfer Uri (instead of file path) when remote end supports it.
     return invokeRpc<ServiceMap>('_flutter.runInView',
       params: <String, dynamic> {
         'viewId': viewId,
-        'mainScript': main.toFilePath(windows: false),
-        'packagesFile': packages.toFilePath(windows: false),
-        'assetDirectory': assetsDirectory.toFilePath(windows: false)
+        'mainScript': main.toString(),
+        'packagesFile': packages.toString(),
+        'assetDirectory': assetsDirectory.toString()
     });
   }