terminal: Add Alt key bindings for terminal

[CharlesChen0823]

• Fixes: Terminal: emacs shortcuts not working: alt-f, ctrl-f, alt-b, etc. #14543

Release Notes:

• Improve Terminal compatibility with emacs-style meta (alt/option) shortcuts. (#14543, thanks @CharlesChen0823)

[notpeter]

@CharlesChen0823 Thank you for doing this and apologies for the delayed review.

I noticed that emacs query replace (M-%) was also broken in Terminal so I made additional changes to support that and the rest of the default emacs key bindings.

[notpeter]

Turns out that change is unnecessary and this can be controlled via terminal.option_as_meta in settings.

In #15535 I'm reverting this and changing the option_as_meta default to true.
This will land in Zed Preview later today and in Zed Stable in a week (2024-08-06).

Until then you can add the following to your settings:

  "terminal": {
    "option_as_meta": true
  },