Make it possible to rebind the Confirm keybinding

[stefanhaller]

PR Description

Remapping keybinding.universal.confirm from <enter> to something like y is currently impossible because the same keybinding is also used to confirm prompts (e.g. "New branch") and the search prompt. Fix this by hard-coding enter for those; it doesn't really make sense to use any other key for prompts.

While at it, add separate bindings for confirmMenu and confirmSuggestion for those who would like to have different keys for these. Of these, confirmMenu could be a little tricky because menus are sometimes used purely as a choice (e.g. in "Amend commit attribute" or the global keybindings menu), in which case you might want to use <enter>, but other times as a substitute for a confirmation (e.g. for "Delete branch"), in which case you might want to remap to y. I don't have a great idea what to do about that, to be honest. Feedback welcome.

In this PR we only take care of Confirm, which many people seem to be concerned about. We might consider doing something similar for Esc, but it seems less urgent, and I'm out of time now. 😄

This seemingly simple change required some serious refactoring under the hood, so thorough testing would be good to ensure we didn't break anything.

Closes #2611
Closes #2767
Closes #3471

Related: #2768

[codacy-production]

Coverage summary from Codacy

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Coverage variation	Diff coverage
Report missing for 94aa1101	✅ 94.12%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (94aa110)	Report Missing	Report Missing	Report Missing
Head commit (b3a3410)	57738	50192	86.93%

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Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#4860)	204	192	94.12%

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[AndrewSav]

You do not emumerate the list of dialogs/prompts it will apply to, so I'm not sure if it will also close #2009. Please advise? Thank you for your work.

[stefanhaller]

You do not emumerate the list of dialogs/prompts it will apply to, so I'm not sure if it will also close #2009. Please advise? Thank you for your work.

It applies to all popups that show a message (not editable, not a menu); that's why the keybinding is called universal.confirm. If you change it, it will not only affect the force-push prompt, but all other confirmations, and even popups that are purely informational and don't offer a choice (e.g. bisect finished).