Add back granularity: "line"? about proposal-intl-segmenter

[littledan]

The motivation for leaving out line is documented in the Readme. It wasn't really about the issues you raised, and I think the reasons there still argue for omitting it.

[gibson042]

Per November 2018 ECMA-402 meeting notes and #49 , granularity: "line" was removed because of concerns about reimplementing paragraph layout. But as @FrankYFTang and others noted in those conversations, line break opportunities are useful for other purposes. https://twitter.com/AaronPresley/status/1116424359223054336 presents such an example.

However, these points were conceded in January (though I don't believe we ever heard back on line breaking in Houdini). I'll close this to avoid relitigation.

[littledan]

I think it's really valuable to have solutions that several implementers can all be on board with, and it sounds like we have a path towards this within Houdini. If Houdini doesn't deliver on this in a couple years (the estimate @tabatkins gave at the time), I think it'd be worth revisiting in the ECMA-402 group.