feat(markdown): add proseWrap: "preserve" option

[ikatyang]

Fixes #3302

Since detecting sentences in different natural languages is hard, preserving original linebreaks should be a good alternative.

Ref: #3302 (comment)

[azz]

Maybe this should be the default? Currently proseWrap: true causes issues in BitBucket server because its version of Markdown is much more sensitive to line breaks.

[ikatyang]

It will be an actual breaking change if we change the default, though the change is to preserve linebreaks, not sure if we should do so.

[azz]

@vjeux Thoughts on making this the default?

[vjeux]

I am not a fan of the current default, breaking words to 80 columns for markdown is imo a bad idea. Honestly I think that the best default would be to put everything in one line, but making preserve would be a step in the right direction from my point of view.

[azz]

Might want to update playground as well?

[ikatyang]

The playground option should be in another PR, tracked in #3338.

[SimenB]

So this basically means prettier won't touch paragraphs all all? If so I'd prefer the default being all in a single line - I expect prettier to normalize stuff not just ignore inconsistencies.

I do think this option is a good alternative, but I do think the value proposition of either of the two existing options are higher

[ikatyang]

I originally choose "always" by default as it looks the most "prettier"-style, wrapping everything fits the printWidth, but if we're talking about the correctness, "preserve" should be the best since the markdown renderer used by GitHub comment/BitBucket are linebreak-sensitive, or if we're talking about which one is the most useful, it should be "never".

I don't have strong preference here.

[suchipi]

My vote goes towards making "preserve" the default.

[azz]

@SimenB In principle I agree, but unfortunately (as @ikatyang mentioned) there are multiple variants of Markdown that are all a little different when it comes to line breaks, so, to me, favouring not breaking the rendering of existing Markdown makes sense for the default value.

[azz]

Do we still use deprecated.js? It seems to be outdated.

[ikatyang]

It seems it's only used for useFlowParser warning.

I think we can refactor those option warnings/redirections using #3352.

[azz]

LGTM.