Allow Hash object reuse

### What is the problem this feature will solve? https://github.com/nodejs/node/issues/25857#issuecomment-466384613 I'm creating the hash of many small objects and need to keep track of these individual hashes so https://github.com/nodejs/node/issues/29903 doesn't work. My specific use case is that I'm hashing directory layouts to setup a file layout that's optimal about symlinking entire directories when its filled with symlinked entries that all point to the same source directory. I can get into specifics if that matters. ### What is the feature you are proposing to solve the problem? crypto.Hash.reset() - reset the internal state of the hasher and allows it to be reused with any new allocations ### What alternatives have you considered? -not use crypto.hash in this case and write my own hasher -create a native add on that lets me manage to hash context according to my needs