feat: Fixed animating new tabs and improved compact mode correctness, b=no-bug, c=common, compact-mode

src/zen/common/modules/ZenUIManager.mjs

@@ -877,7 +877,7 @@ window.gZenVerticalTabsManager = {
           {
             opacity: [0, 1],
             transform: ['scale(0.95)', 'scale(1)'],
-            marginBottom: isLastItem() ? [] : [transform, '0px'],
+            marginBottom: isLastItem() ? ['0px', '0px'] : [transform, '0px'],
           },
           {
             duration: 110,

src/zen/compact-mode/ZenCompactMode.mjs

@@ -720,7 +720,7 @@ window.gZenCompactModeManager = {
           MousePosTracker._callListener({
             onMouseEnter: () => (isHovered = true),
             onMouseLeave: () => {},
-            getMouseTargetRect: () => window.windowUtils.getBoundsWithoutFlushing(target),
+            getMouseTargetRect: () => target.getBoundingClientRect(),
           });
           // Let's double check if the mouse is still hovering over the element, see the bug above.
           if (isHovered) {