feat: accept-all option for autocomplete

[AllanChain]

By default, when inputting LaTeX commands, accepting suggestion is done by [Tab] (accept-suggestion), and exiting to math mode is done by [Enter] (accept).

This PR adds a accpet-all option to autocomplete, which does both accept-suggestion and accept. If there are no suggestions, only accept is done. This allows users to bind keys to accept suggestion and exit latex mode at the same time, which is convenient. (which is also consistent with LyX if you know it)

[arnog]

Thanks for the PR. That's an interesting idea.

Do you think a default keybinding should use that option?

[AllanChain]

While I'm conservative for behavior changes, I personally appreciate the "Tab to cycle and Enter to accept and exit to math" way.

And I have to point out that if it is made default, there are some rare edge cases where the user intended \al (just an example) and the suggestions only list \aleph etc., and the user is impossible to input \al.

BTW, I'm developing and using MathLive plugin for Logseq, where the user can always change the keybinding using the config file. Therefore whether enabling this by default will not make much difference for me.