Improve completion, action and shared project popovers' layout (#4226)

Before:

* cutoff completion labels and docs
<img width="801" alt="image"
src="https://github.com/zed-industries/zed/assets/2690773/12fe39b2-a8a7-42d8-b697-e2a4fbd836b7">

* too long action labels start to introduce newlines and break the
layout
<img width="716" alt="image"
src="https://github.com/zed-industries/zed/assets/2690773/a0530f1e-4200-4cc4-8e0f-9a63d04e4d5c">

* too long completion proposals are cut off
<img width="1321" alt="image"
src="https://github.com/zed-industries/zed/assets/2690773/1ec154a1-9de5-4e47-9e9f-632b3e33f42a">



After:

* the docs are shifted, but both completions and docs are rendered
entirely now
<img width="1351" alt="image"
src="https://github.com/zed-industries/zed/assets/2690773/ddb0baa4-88b6-45e9-b3e1-496c0d6a0d0f">

* 
<img width="750" alt="image"
src="https://github.com/zed-industries/zed/assets/2690773/102ed77c-d7d0-41d2-a4a0-a8c73285ea8a">

* completions are not jumping in sized anymore, with all elements
aligned to occupy max elements' width and height
<img width="1459" alt="image"
src="https://github.com/zed-industries/zed/assets/2690773/483e3534-b00a-423c-a848-3c4ca1199510">


Release Notes:

- Improved completion and action label layouts