Separate 'brace action' and 'match selection' in keymap

[asvln]

This changes the behavior of m to only match selections.
m = mi
M = ma
Brace actions are relocated to ^.

Issue: #3852

[the-mikedavis]

I like the idea of easier access to mi/ma.

I don't like relocating brace actions to ^ though. ^ has been proposed and tried for a few Kakoune keymaps (marks, mawww/kakoune#1116) but it has never stuck. It's not very discoverable. (Plus I'd like to use it for marks/selections #3720 :P)

The normal-mode keymap is already very full which is why it's hard to separate key sequences like m out like this.

[asvln]

I like the idea of ^ being reserved for marks also.

I do think brace functionality deserves it's own key rather than being nested under another diag.

[dead10ck]

I am also not a fan of ^. This also breaks the "in" / "around" mnemonic. I don't think this is worth saving a single keystroke.

[asvln]

moved to #4655