add support for 1:many source-maps

[bcoe]

we should add support for source-maps that map from one transpiled source to many original sources, this is an extension to the work done in #19.

[scythargon]

Hi! Is this related? jestjs/jest#8596
I mean, seeing the progress on that Jest PR - will it help with this one?

[bcoe]

@scythargon I don't think that the 1:many issue is specifically blocking Jest; this relates to the specific use case of combination, so if you have foo.js, bar.js, and then deploy a source file that's bar.js + foo.js.

[felixfbecker]

This is needed if any bundler like webpack is used

[lukeapage]

I started trying to hack this in to get to poc stage:
lukeapage@c169da3

but I'm pretty close to giving up - the above appears to work but I don't understand why lines start with a count of 1 - I'll try to continue bashing my head against it. also not sure if the issues I am having are down to the fact I'm using output from playwright, piped through pupeteer-to-istanbul.

[lukeapage]

Would appreciate feedback and testing on #91
It turned out pupeteer/playwright output is screwed, but getting the raw v8 output and piping it in worked well.