Make staging/unstaging keybinding consistent

[kuychaco]

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Description

@as-cii kindly pointed out that with the new in-editor diff view our key-bindings for staging/unstaging are inconsistent between the diff view and the staging view.

Previously enter staged/unstaged changes in the diff view. Since we converted this view to use an editor and we hope to implement editable diffs, we'll want enter to have its default behavior of entering new lines.

#1512 re-mapped the commands for staging/unstaging changes in the diff view to cmd-enter. In the git panel we are still using enter to stage/unstage files.

Other relevant keybindings include

• o to open file and jump to line
• delete to discard line
• any others?

We want consistency across our UI, so here's what I propose:

• add back previous keybindings to diff view. they are unused anyway because diffs are not yet editable. we can keep the cmd-... keybindings as well
• cherry-pick these changes to beta so that users on stable never lose their keybindings
• when we ship editable diffs
  • remove the non-cmd keybindings in the diff view
  • convert staging view keybindings to use the cmd- variants for consistency
  • let users know about change with a notification?
  • in staging view, use enter to open diff view for selected file. currently this is mapped to cmd-left which is not super intuitive/discoverable

[as-cii]

Thanks for opening this, @kuychaco! Yesterday I accidentally created a commit in the following scenario:

• I typed a commit message
• I wanted to unstage some file that didn't belong in the commit
• To do that, I mistakenly pressed ⌘⮐ which created a commit

So I am definitely experiencing some pain due to the inconsistency. I could easily undo the commit (thanks to the awesomeness of this package) but I agree it would be nice to have a consistent scheme between views. 👍