Add text indentation support at paragraph block type level

[kjellr]

Currently, paragraphs in the editor have vertical space to differentiate one paragraph from the next:

To allow for an optional, more "literary" treatment, we should consider adding an option to Global Styles that would collapse that margin and instead use indentation to differentiate from one paragraph to the next:

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Similar: #12451

[mtias]

Yes! I'd been wanting to do this for a while, but needed more of the global styles infrastructure in place. I also want to allow justification (with localized hyphens and such) to happen at this level globally so it can be undone easily.

It can also be an opportunity to include some other typographical flair, depending on what the fonts support (discretionary ligatures, etc).

[skorasaurus]

related #34688

[ericmacknight]

Yes, please!

[justintadlock]

Just adding a +1 here. For folks like me who have some literary or academic work and want to preserve formatting, having a way to text-indent paragraphs would be super helpful.

I've been shipping an indent block style in my theme work to take care of this need (in case anyone needs a solution in the meantime): https://gist.github.com/justintadlock/257087c52e46272f1445fd8ff60c8d83