Add API to determine output file names

[ajafff]

Given a fileName and a CompilerOptions object, determine the output file name(s).
It also needs an API to determine the output file name(s) for projects with outFile.

This requires another helper function to determine the inferred or declared rootDir of a given config.

Needed for fimbullinter/wotan#392
Related: microsoft/TypeScript#26410

[ajafff]

maybe add an option to include sourceMaps as well if they are enabled in CompilerOptions and not inlined

[ajafff]

The logic for handling output file names of project references is currently added directly to Fimbullinter.
There will be much more work for the case where rootDir is not set (either explicitly or via composite) as it needs all file names and compute the common source directory. Currently I don't need such functionality. If there's demand for it, I'll add it though.