Add `code_action_picker` command

[John-Toohey]

Fixes #3502, adding a separate command code_action_picker which opens code_action but in a picker, allowing for searching.

An Asciinema recording

Apologies for my slow computer loading lsp in this recording, but here is a demonstration of the functionality provided by this MR:

Asciinema recording; lsp loads at 0:25

[John-Toohey]

Okay, I have fixed the PR to fix the workflow. Clippy is now happy.