12x faster resolver cache

[devongovett]

This rewrites the resolver cache to be much more efficient. Instead of storing data in a bunch of separate hash maps, this creates a new CachedPath data structure that stores information about paths in a single place. This includes a direct reference to the parent path, a pre-computed hash of the path, lazily loaded file kind (e.g. file/dir/symlink), canonical path, and parsed package.json/tsconfig.json. CachedPath references this info via an Arc, so it is cheap to compare, hash, and clone compared with a PathBuf. It can also perform common operations like appending a sub-path or file extension cheaply via a reusable thread local scratch path, avoiding intermediary allocations.