Collapsible imports

[JosephKiranBabu]

Allow zed editor to collapse import statements like in vim/neovim. This should be possible in 2 ways:

1. Pressing z a in vim mode
2. A collapse arrow button in the gutter.

I checked only in TypeScript that imports are not collapsible. I didn't check other programming languages.

[pelykh]

Same in #30763. You can hide imports by selecting imports and running editor:fold selected ranges command as a workaround, but it's annoying to do each time.