testing: use overflow ellipsis in test tree (microsoft#186806)

* tree: add fast path for children updates in compressedObjectTreeModel

I noticed in testing that more things were getting rerendered than they
should have been. This adds a fast path so that, if the elements in
a compressed node don't change when its children are updated, we only
update the children instead of replacing the entire node from the parent
collection.

* testing: use overflow ellipsis in test tree

Fixes microsoft#186320

Had to abandon flexbox for this, so do manual tweaks to make codicons show nicely:

![](https://memes.peet.io/img/23-06-321bf892-8f69-4548-9c76-465f33205c8e.png)

Author: connor4312

src/vs/workbench/contrib/testing/browser/media/testing.css

@@ -43,13 +43,19 @@
 
 .test-explorer .test-item .label,
 .test-output-peek-tree .test-peek-item .name {
-	display: flex;
-	align-items: center;
 	flex-grow: 1;
-	gap: 0.15em;
 	width: 0;
 	overflow: hidden;
 	white-space: nowrap;
+	text-overflow: ellipsis;
+}
+
+.test-output-peek-tree .test-peek-item .name .codicon,
+.test-explorer .test-item .label .codicon {
+	vertical-align: middle;
+	font-size: 1em;
+	transform: scale(1.25);
+	margin: 0 0.125em;
 }
 
 .test-explorer .test-item,
@@ -108,15 +114,6 @@
 	margin: 0;
 }
 
-.test-explorer .name,
-.test-output-peek-tree .name {
-	overflow: hidden;
-	text-overflow: ellipsis;
-	flex-grow: 1;
-	height: 22px;
-	align-items: center;
-}
-
 .test-explorer .computed-state,
 .test-output-peek-tree .computed-state {
 	margin-right: 0.25em;