[Synthetic shadow] Memory leak when clicking on element

[nolanlawson]

When using @lwc/synthetic-shadow, a component rendering a <h1> will leak if that <h1> is clicked. This does not repro if the <h1> is not clicked, and it does not repro if @lwc/synthetic-shadow is not being used.

Minimal repro

Repro steps:

1. Clone the above commit
2. pnpm i && pnpm run dev
3. Open localhost:3000
4. Click "Add"
5. Click the "Hello world" <h1>
6. Click "Remove"
7. Take a Chrome Memory snapshot in the DevTools
8. Notice that 10MB is being allocated and <x-app> is leaked

I can also reproduce this in Firefox.

[git2gus[bot]]

This issue has been linked to a new work item: W-17274024