Text transformation: Allow reverting by pressing backspace

[Reinmar]

📝 Provide a description of the improvement

Currently, we allow reverting an automatic transformation result by pressing undo. It's a separate undo step.

However, it's common among other editors to also allow reverting text transformation by pressing backspace immediately after transformation happened.

It works this way in GDocs and Word:

1. Type "1/2"
2. Type space
3. It gets converted to "½ "
4. Press backspace
5. You get: "1/2 "

Note: It's super smart in Word where this 1/2 never gets converted back to a fraction again, even if you remove that space and type it again. However, GDocs doesn't implement this mechanism and you can again trigger transformation again by typing another space. We can do KISS as both options make some sense, plus going in a Word-like direction would require more work.

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[Reinmar]

Note: In GDocs and Word backspace behaves like undo – this is – you can redo that change.

Note: What about autolinking, auto media embed, etc.

[Reinmar]

• Features to work this way (included in the scope of this ticket):
  • Text transformation
  • Auto linking
  • Auto media embed (pasting a URL to embed)
  • Auto image
  • Autoformat (??? we're not sure about this one)
• Flow:
  • A certain feature (the one that does the transformation) sets the flag (probably via a method) on the Delete plugin. It needs to be set in a way that it's not going to be reverted immediately, in the same batch of changes that are caused by the transformation itself.
  • The Delete plugin takes care of resetting that flag back to false on the next model change (including the selection).
  • If it's still true upon Backspace, trigger the undo command (and reset the flag). This should be handled by the Delete plugin.
• Scope:
  • The logic mentioned above.
  • Covering all 5 features.
  • Integration tests in all 5 features.
• Other funky remarks:
  • Chained transformations

Resolves: #2364.

Also: will resolve the same issue on Mobile where undo may not be that easily available.

[arkflpc]

Are we sure about Autoformat yet?

[Reinmar]

I'd go without autoformat for now because this will be safer. But, it'd be good to test how this works with autoformat to see whether the UX is good or confusing.

Hence, if you could create a PR for the features that we want to cover and then a second draft PR (based on that former PR) for autoformat?

[arkflpc]

PR to test autoformat: #10508