Resizable columns (#34794)

This PR adds resizable columns to the keymap editor and the ability to
double-click on a resizable column to set a column back to its default
size.

The table uses a column's width to calculate what position it should be
laid out at. So `column[i]` x position is calculated by the summation of
`column[..i]`. When resizing `column[i]`, `column[i+1]`’s size is
adjusted to keep all columns’ relative positions the same. If
`column[i+1]` is at its minimum size, we keep seeking to the right to
find a column with space left to take.

An improvement to resizing behavior and double-clicking could be made by
checking both column ranges `0..i-1` and `i+1..COLS`, since only one
range of columns is checked for resize capacity.

Release Notes:

- N/A

---------

Co-authored-by: Anthony <anthony@zed.dev>
Co-authored-by: Remco Smits <djsmits12@gmail.com>

Cargo.lock

@@ -14779,6 +14779,7 @@ dependencies = [
  "fs",
  "fuzzy",
  "gpui",
+ "itertools 0.14.0",
  "language",
  "log",
  "menu",