fix(ui): keep the tree's focus outline when a row is hovered

The row hover rule set an outline shorthand at higher specificity than
both focus outline rules, so hovering the focused row replaced its ring
with 1px dashed transparent. Native's generated list styles skip hover
on selected and focused rows, :hover:not(.selected):not(.focused), and
re-assert state backgrounds on :hover, so hover never repaints or
un-outlines them.

There is also no list.selectionOutline or list.hoverOutline theme color,
only toolbar.hoverOutline; native feeds both list style slots from
activeContrastBorder. Both tokens resolved to transparent in every
theme, high contrast included.

Author: EhabY

packages/ui/src/components/Tree/Tree.css

@@ -57,7 +57,10 @@
 	display: none;
 }
 
-.ui-tree-item:not([aria-disabled="true"]):not([aria-selected="true"])
+/* Native skips hover on selected and focused rows, keeping their outlines. */
+.ui-tree-item:not([aria-disabled="true"]):not([aria-selected="true"]):not(
+		.ui-tree-item--focused
+	)
 	> .ui-tree-item__row:hover {
 	color: var(--ui-list-hover-foreground);
 	background: var(--ui-list-hover-background);

packages/ui/src/tokens.css

@@ -179,15 +179,17 @@
 		--vscode-list-focusOutline,
 		var(--ui-focus-border)
 	);
-	--ui-list-selection-outline: var(--vscode-list-selectionOutline, transparent);
+	/* No list.selectionOutline or list.hoverOutline color exists; native feeds
+	   both from activeContrastBorder. */
+	--ui-list-selection-outline: var(--vscode-contrastActiveBorder, transparent);
 	--ui-list-inactive-focus-outline: var(
 		--vscode-list-inactiveFocusOutline,
 		transparent
 	);
-	--ui-list-hover-outline: var(--vscode-list-hoverOutline, transparent);
+	--ui-list-hover-outline: var(--vscode-contrastActiveBorder, transparent);
 	--ui-list-focus-and-selection-outline: var(
 		--vscode-list-focusAndSelectionOutline,
-		var(--vscode-list-selectionOutline, var(--ui-list-focus-outline))
+		var(--vscode-contrastActiveBorder, var(--ui-list-focus-outline))
 	);
 	/* Outside a webview, approximate the native guides (inactive is the
 	   active stroke at 40%) instead of disappearing. */