@RyanCavanaugh @rbuckton @DanielRosenwasser This change is on top of tsc --b generating .tsbuildinfo. The main change is that tsc --w will use the hash as file version instead of count of changes in lifetime of the span (as otherwise the written signature makes no sense in determining if the file has changed and technically we want all tsc modes to use same version type so its compatible in all modes?).
Its ready for review as well.

@RyanCavanaugh please take a look at this as well since I think having same file version when writing tsbuildinfo is important for things to work correctly and because we don't have published API for tsbuild yet many apis depend on watch api to build the projects and we should not regress there by writing conflicting file versions.