Reduce allocations for a typical patch scenario

For the following typical replace operation

[
    { "op": "replace", "path": "/Name", "value": "Roger Federer" }
]

Before:

After: After making the following couple of changes, I see a 30% reduction in memory usage

Fix the round-tripping issue mentioned here https://github.com/aspnet/JsonPatch/issues/69
Avoid validating the JsonPatchDocument itself (AFAIK this is not required as an end user is not going to validate it but should be validating his model....that said validating the model while patching is an open question currently as we do not validate the model)

aspnet / JsonPatch