[vm/shared] Rename IsolateGroupShared to IsolateGroupBound.

TEST=ci

CoreLibraryReviewExempt: vm-only change
Change-Id: If9c8bbd0e90e4ec1f70742c704ad31fce5681ec1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/441063
Commit-Queue: Alexander Aprelev <aam@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>

samples/ffi/httpIG/lib/http.dart

@@ -27,7 +27,7 @@ Future<String> httpGet(String uri) async {
       },
     );
   final sendPort = rp.sendPort;
-  final callback = NativeCallable<HttpCallback>.isolateGroupShared((
+  final callback = NativeCallable<HttpCallback>.isolateGroupBound((
     Pointer<Utf8> responsePointer,
   ) {
     final typedList = responsePointer.cast<Uint8>().asTypedList(
@@ -60,7 +60,7 @@ late int counter;
 ReceivePort httpServe(void Function(String) onRequest) {
   counter = 0;
   final rp = ReceivePort();
-  final callback = NativeCallable<HttpCallback>.isolateGroupShared((
+  final callback = NativeCallable<HttpCallback>.isolateGroupBound((
     Pointer<Utf8> requestPointer,
   ) {
     counter++;