gpui: Rework overlay element (#9911)

There was a problem using deferred draws with `overlay` and tooltips at
the same time.

The `overlay` element was removed and was split up into two separate
elements
- `deferred`
- `anchored` - Mimics the `overlay` behavior but does not render its
children as deferred

`tooltip_container` does not defer its drawing anymore and only uses
`anchored`.

/cc @as-cii 


Release Notes:
- Fixed tooltip for the recent projects popover not showing anymore

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Co-authored-by: Antonio <antonio@zed.dev>