While debugging the mempool issue (#5796), I've noticed we're spending
quite a bit of time encoding blobs of data, which never get printed! The
reason is filtering occurs on the level below, so Go runtime rightfully
evaluates function arguments.
I think it's okay to not format raw bytes.
## Description
This PR wraps the stdlib sync.(RW)Mutex & godeadlock.(RW)Mutex. This enables using go-deadlock via a build flag instead of using sed to replace sync with godeadlock in all files
Closes: #3242
## Description
partially cleanup in preparation for errcheck
i ignored a bunch of defer errors in tests but with the update to go 1.14 we can use `t.Cleanup(func() { if err := <>; err != nil {..}}` to cover those errors, I will do this in pr number two of enabling errcheck.
ref #5059
Migrates the `rpc` package to use new JSON encoder in #4955. Branched off of that PR.
Tests pass, but I haven't done any manual testing beyond that. This should be handled as part of broader 0.34 testing.