Properly handle Windows file: URLs on Node.js

This adds logic to the JS implementation of URI to determine whether
the code is running on Windows under Node.js.

Author: nex3

pkg/dev_compiler/tool/input_sdk/patch/core_patch.dart

@@ -602,7 +602,10 @@ class Uri {
 @patch
 class _Uri {
   @patch
-  static bool get _isWindows => false;
+  static bool get _isWindows => _isWindowsCached;
+
+  static final bool _isWindowsCached =
+      JS('bool', 'process !== undefined && process.platform == "win32"');
 
   // Matches a String that _uriEncodes to itself regardless of the kind of
   // component.  This corresponds to [_unreservedTable], i.e. characters that

sdk/lib/_internal/js_runtime/lib/core_patch.dart

@@ -611,7 +611,10 @@ class Uri {
 @patch
 class _Uri {
   @patch
-  static bool get _isWindows => false;
+  static bool get _isWindows => _isWindowsCached;
+
+  static final bool _isWindowsCached =
+      JS('bool', 'process !== undefined && process.platform == "win32"');
 
   // Matches a String that _uriEncodes to itself regardless of the kind of
   // component.  This corresponds to [_unreservedTable], i.e. characters that