Fixed DDRIT failure (dotnet#25551)

* made sure we raise workspace changed events even when there is no text change.

this is needed to bring workspace up to date with latest text snapshot after we don't merge 2 text snapshot to 1 source text if content is same.

see this for more detail - dotnet#24849

* added comments on why we need to process all text change events

src/EditorFeatures/Text/Extensions.TextBufferContainer.cs

@@ -100,18 +100,24 @@ public override SourceText CurrentText
             private void OnTextContentChanged(object sender, TextContentChangedEventArgs args)
             {
                 var changed = this.EtextChanged;
-                if (changed != null && args.Changes.Count != 0)
+                if (changed == null)
                 {
-                    // this should convert given editor snapshots to roslyn forked snapshots
-                    var oldText = (SnapshotSourceText)args.Before.AsText();
-                    var newText = SnapshotSourceText.From(args.After);
-                    _currentText = newText;
-
-                    var changes = ImmutableArray.CreateRange(args.Changes.Select(c => new TextChangeRange(new TextSpan(c.OldSpan.Start, c.OldSpan.Length), c.NewLength)));
-                    var eventArgs = new TextChangeEventArgs(oldText, newText, changes);
-                    this.LastEventArgs = eventArgs;
-                    changed(sender, eventArgs);
+                    return;
                 }
+
+                // we should process all changes even though there is no text changes
+                // otherwise, Workspace.CurrentSolution won't move forward to latest ITextSnapshot
+
+                // this should convert given editor snapshots to roslyn forked snapshots
+                var oldText = (SnapshotSourceText)args.Before.AsText();
+                var newText = SnapshotSourceText.From(args.After);
+                _currentText = newText;
+
+                var changes = ImmutableArray.CreateRange(args.Changes.Select(c => new TextChangeRange(new TextSpan(c.OldSpan.Start, c.OldSpan.Length), c.NewLength)));
+                var eventArgs = new TextChangeEventArgs(oldText, newText, changes);
+
+                this.LastEventArgs = eventArgs;
+                changed(sender, eventArgs);
             }
 
             // These are the event args that were last sent from this text container when the text