alacritty: add CSIu support

[blaggacao]

Description

Add CSIu support for alacritty

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all. (fails unrelated on my machine)

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

[berbiche]

Thanks for the contribution!

[blaggacao]

@berbiche Thank you for your review, could you have a look again? Please feel free to directly amend this PR if you have an idea to encode those CSIu datapoints into a generic module that could be re-utilized across terminals (that support it).

[berbiche]

LGTM!

Need to revisit this

[blaggacao]

This is blocking: divnix/digga#51

[berbiche]

@blaggacao can you add a simple test case where the user has enabled CSIu support while using their own keybindings? (i.e. CSIuSupport = true; and programs.alacritty.settings.key_bindings = [ { .... } ];.

The merging should work fine but it's always nice to have a test case for this!

[stale]

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