This PR makes json_op_sync/async generic to all Deserialize/Serialize types
instead of the loosely-typed serde_json::Value. Since serde_json::Value
implements Deserialize/Serialize, very little existing code needs to be updated,
however as json_op_sync/async are now generic, type inference is broken in some
cases (see cli/build.rs:146). I've found this reduces a good bit of boilerplate,
as seen in the updated deno_core examples.
This change may also reduce serialization and deserialization overhead as serde
has a better idea of what types it is working with. I am currently working on
benchmarks to confirm this and I will update this PR with my findings.