add a :select-register typable command

[savente93]

I've been mucking about with macros and doing some cool things. One thing that I was missing was the ability to select registers from my config.toml keybindings. I'm aware of some prior art (#1383, #8958) about this. While having a :select-register typable command wouldn't fully solve #1383 I think it would enable a lot of workflows I've seen people mention there such as yanking to temporary registers when moving lines up or down.

I feel like this would also be really quite simple to implement, and I'd be happy to open a PR for this if maintainers are open to merging it. Thoughts?

[the-mikedavis]

See #10609, macro keybindings are the intended solution for this rather than a new command