Unify pasting UI

[f1ames]

Type of report

Feature request

Provide description of the new feature

Extracted from #3258:

Unified paste handling can also benefit from some unified UI. I'm mostly thinking of utilizing splitbutton (#1766) for it. Instead of many paste buttons, we can have in fact two: normal paste button and special paste button (or even further reduce it to one paste button, just like Word does). Special paste button will be a split button with several options:

• Paste from Word (default one),
• Paste from GDocs,
• Paste as plain text,
• some other Paste from Anything.

I realize that it would require resuming work on splitbutton plugin, but TBH I think it's worth it. OTOH middleware architecture can be introduced without introducing also unified UI.

☝️ #3258 (comment)

About UI - I believe our users are not interested in the source of the paste content. When I'm copying RTF from Gdocs, Word or any other source, I just want to preserve formatting during paste. Additional buttons for each paste type just introduces complexity for something dumb simple (I mean copy/paste use case, not internal mechanism). I would rather simplify naming by renaming Paste from World into Paste / Paste Rich Text. Overall, I'm not sure why we distinguish Paste and Paste from World currently - have a feeling that it should be just Paste (keep formatting, doesn't matter the source) and Paste as plain text. End users are rather not interested in internals.

Paste Rich Text should be smart enough to choose correct handler for me - I believe that was the big point of the whole refactoring. Simplifying paste mechanism for end users.

☝️ #3258 (comment)

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The proposal here is to simplify pasting UI to have only two paste buttons: Paste and Paste as plain text. Regular paste button should be "smart" enough to handle pasting from different apps like Word, Excel and Google Docs.

My only concern is that, after this change some users may start to think that we dropped support for paste from Word (like after dropping paste dialog - #469) - so it needs to be clearly communicated that the UI was simplified while the underlying architecture/implementation got "smarter".