Revert "Improve completion, action and shared project popovers' layout" (#4233)

Reverts zed-industries/zed#4226

Unfortunately there where some worse states possible after this PR.
Reverting until after the launch, as the problems it addresses are still
bad.

![Screenshot 2024-01-23 at 3 20
59 PM](https://github.com/zed-industries/zed/assets/2280405/d25ab0d5-db49-44cb-b865-e320a97616ce)