Make RegExpMatch.pattern have type RegExp.

It's always a RegExp, so it's a safe change.
It's also a very, very rarely used property,
since nobody ever noticed that it wasn't typed optimally.

Tested: Type change of getter to actual type of value. No new test.
CoreLibraryReviewExempt: Aske is out.
Change-Id: Ifb560a80c3cdb05be0164c593383539dc10ec0dd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/267961
Reviewed-by: Stephen Adams <sra@google.com>
Reviewed-by: Nate Bosch <nbosch@google.com>
Commit-Queue: Lasse Nielsen <lrn@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>

CHANGELOG.md

@@ -31,6 +31,7 @@
 #### `dart:core`
 - Added `bool.parse` and `bool.tryParse` static methods.
 - Added `DateTime.timestamp()` constructor to get current time as UTC.
+- The type of `RegExpMatch.pattern` is now `RegExp`, not just `Pattern`.
 
 - **Breaking change** [#49529][]:
   - Removed the deprecated `List` constructor, as it wasn't null safe.

sdk/lib/_internal/js_dev_runtime/private/regexp_helper.dart

@@ -180,7 +180,7 @@ class JSSyntaxRegExp implements RegExp {
 }
 
 class _MatchImplementation implements RegExpMatch {
-  final Pattern pattern;
+  final RegExp pattern;
   // Contains a JS RegExp match object that is an Array with extra "index" and
   // "input" properties. The array contains Strings but the values at indices
   // related to capture groups can be undefined.

sdk/lib/_internal/js_runtime/lib/regexp_helper.dart

@@ -168,7 +168,7 @@ class JSSyntaxRegExp implements RegExp {
 }
 
 class _MatchImplementation implements RegExpMatch {
-  final Pattern pattern;
+  final RegExp pattern;
   // Contains a JS RegExp match object.
   // It is an Array of String values with extra 'index' and 'input' properties.
   // If there were named capture groups, there will also be an extra 'groups'

sdk/lib/_internal/vm/lib/regexp_patch.dart

@@ -117,7 +117,7 @@ class _RegExpMatch implements RegExpMatch {
 
   int get groupCount => _regexp._groupCount;
 
-  Pattern get pattern => _regexp;
+  RegExp get pattern => _regexp;
 
   String? namedGroup(String name) {
     var idx = _regexp._groupNameIndex(name);

sdk/lib/_internal/wasm/lib/regexp_helper.dart

@@ -163,7 +163,7 @@ class JSSyntaxRegExp implements RegExp {
 }
 
 class _MatchImplementation implements RegExpMatch {
-  final Pattern pattern;
+  final RegExp pattern;
   // Contains a JS RegExp match object.
   // It is an Array of String values with extra 'index' and 'input' properties.
   // If there were named capture groups, there will also be an extra 'groups'

sdk/lib/core/regexp.dart

@@ -483,4 +483,6 @@ abstract interface class RegExpMatch implements Match {
 
   /// The names of the named capture groups of [pattern].
   Iterable<String> get groupNames;
+
+  RegExp get pattern;
 }