Always use absolute paths after reading from cache

[mistic]

We only want to use relative paths when writing to cache with a cacheContext.
In all the other cases, right after reading from cache, we should always use absolute paths or the webpack watch will break in very strange ways (probably because a bug in chokidar/watchpack). In that case, using a relative path with this.fs.stat (the fs cached version from the webpack compiler) would return stale metadata.

/CC @evilebottnawi

[alexander-akait]

Can we add tests for this? I know it is not easy, but will be great have tests and note/todo in source code because for future developers/contributors it will be hard to understand why we did it and they can break it again

[mistic]

@evilebottnawi I've made the changes you request, could you review the PR please?

[alexander-akait]

Can we open issue in https://github.com/webpack/memory-fs?

[mistic]

@evilebottnawi I've opened an issue here #86 if u want to proceed with further investigation in the underlying dependencies