Backportable keymap changes

[smashwilson]

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Description of the Change

Restore MultiFilePatch navigation keybindings unadorned by cmd or ctrl that were removed by #1512. Specifically:

• right and cmd-right or ctrl-right surface focus to the Git tab
• backspace discards the selection
• enter stages or unstages the selection
• o jumps to file
• / toggles between line and hunk selection mode

I've also separated the cmd and ctrl keybindings throughout the keymap by platform, guarding cmd bindings with .platform-darwin and ctrl alternatives with .platform-linux, .platform-win32. This opens up the ctrl- bindings on macOS in the future and prevents ambiguities in the binding that we render on buttons and tooltips.

Alternate Designs

Another alternative that we talked about was showing a notification the first time that you try to use one of the deprecated keystrokes (and letting the keystroke go through to the editor normally). I think we should do that as part of the diff editability work, personally.

Benefits

This keeps our keybinding changes from breaking users' muscle memory for another few releases.

Possible Drawbacks

If anyone on macOS learned the ctrl- keystrokes for some reason, those will be broken by this.

It also gives us a lot of redundancy in our keymap, which hurts maintainability. Hopefully this is just a temporary thing.

Applicable Issues

Related to #1820.

Metrics

Out of scope for the moment.

Tests

Our existing test suite should catch any regressions here.

Documentation

The flight manual already references unadorned keystrokes, which is a good reason to backport this. I've also already filed atom/flight-manual.atom.io#504 to update it to use the cmd or ctrl prefixes where appropriate, which we can merge while both work, so that new users learn the prefixed commands instead.

Release Notes

• Restored unprefixed keyboard navigation commands to file patches in the GitHub package.

User Experience Research (Optional)

n/a

[codecov]

Codecov Report

Merging #1847 into master will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1847      +/-   ##
==========================================
+ Coverage   90.85%   90.91%   +0.05%     
==========================================
  Files         195      195              
  Lines       10727    10727              
  Branches     1570     1570              
==========================================
+ Hits         9746     9752       +6     
+ Misses        981      975       -6

Impacted Files	Coverage Δ
lib/controllers/editor-conflict-controller.js	95.95% <0%> (+1.01%)	⬆️
lib/atom/decoration.js	86.74% <0%> (+2.4%)	⬆️
lib/models/conflicts/side.js	96.87% <0%> (+4.68%)	⬆️

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[annthurium]

thanks for fixing this, @smashwilson !

I agree that we should cherry pick this into stable to avoid thrash with key bindings which would frustrate our users.