Optimize CacheFSInfo

CacheFSInfo currently uses a single cache, and delegates to the non-caching getCanonicalFile/exists/isDirectory/isFile the first time any of those methods is called. Using separate caches avoids some unnecessary work.

Also, exists/isDirectory/isFile can be implemented with a single call to get a BasicFileAttributes instead of three separate calls.

Improving those details was observed to improve performance for compilations with very long classes.