Input for popups

[YeungOnion]

There's an essentially complete PR #4189 for keybind scrolling in the picker preview and we've got lsp popup keybind scrolling already, but I think there's still something missing about inputs for popups and I want others' input on what generally should work for popups. I'd find value in:

• a way to move popup text into a buffer would be convenient,
• less surprising mouse support - while I don't expect is largely adopted, the current behavior I see is odd. Described below.

odd mousing with popups

I'm on helix 23.05 (7f5940be) through WSL with Windows Terminal on my Windows machine and the same helix in Tilix on Ubuntu jammy
I found it unexpected that in a popup, the mouse ignores doesn't interact with the popup nor does interaction outside the popup close the popup. Below are instances I find this in, but I'd imagine it appears in all popups.

• picker: both in search and preview
• lsp popup: docs and completion