[DevTools] Render selected outline on top of every other rect (#35012)

When rects are close together (or overlapping) the outline can end up
being covered up by sibling rects or deeper rects. This renders the
selected outline on top of everything so it's always visible.

<img width="275" height="730" alt="Screenshot 2025-10-29 at 8 43 28 PM"
src="https://github.com/user-attachments/assets/69224883-f548-45ec-ada1-1a04ec17eaf5"
/>
<img width="266" height="737" alt="Screenshot 2025-10-29 at 8 58 53 PM"
src="https://github.com/user-attachments/assets/946f7dde-450d-49fd-9fbd-57487f67f461"
/>

Additionally, this makes it so that it's not part of the translucent
tree when things are hidden by the timeline. That way it's easier to see
what is selected inside a hidden tree.

<img width="498" height="196" alt="Screenshot 2025-10-29 at 8 45 24 PM"
src="https://github.com/user-attachments/assets/723107ab-a92c-42c2-8a7d-a548ac3332d0"
/>
<img width="571" height="735" alt="Screenshot 2025-10-29 at 8 59 06 PM"
src="https://github.com/user-attachments/assets/d653f1a7-4096-45c3-b92a-ef155d4742e6"
/>