Fix Collect Report functionality

When language server is started through dartdev is gets
classified as a system isolate, but Collect Report
only looks at user isolates.

I have looked at various ways to fix this but it is
complicated because we are in the middle of rewiring
dartdev to work with AOT built tools.

I would like a trivial change that can be easily
cherry-picked into stable release. Thus I am opting in
to simply change data collection code to collect information
from both user and system isolates.

Change-Id: I00f9eb937153fc730feccf778e5cd2f69d222a18
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/393341
Reviewed-by: Konstantin Shcheglov <[email protected]>
Commit-Queue: Slava Egorov <[email protected]>

Author: mraleph

pkg/analysis_server/lib/src/status/diagnostics.dart

@@ -525,7 +525,7 @@ class CollectReportPage extends DiagnosticPage {
 
       var isolateData = [];
       collectedData['isolates'] = isolateData;
-      var isolates = vm.isolates ?? [];
+      var isolates = [...?vm.isolates, ...?vm.systemIsolates];
       for (var isolate in isolates) {
         String? id = isolate.id;
         if (id == null) continue;