Update newtonsoft.json from 11.0.2 to 13.0.1

[davidmrdavid]

This will remove certain static analysis warnings due to vulnerabilities. At runtime, our dependency is already being replaced with the newtonsoft.json version brought in by WebJobs, which is already 13.0.1, so this change should be safe.

The change also required that we update the code in a few places to account for the possibility of the deserialization returning null. You will a few types being updated to include the ? modifier as a result.

[cgillum]

LGTM, though I wouldn't be surprised if we had some test projects that also needed to be updated.

[cgillum]

It's probably better to just remove this entirely since it's picked up transitively from DurableTask.Core.

[davidmrdavid]

Ah, good idea. Will do

[cgillum]

At runtime, our dependency is already being replaced with the newtonsoft.json version brought in by WebJobs, which is already 13.0.1, so this change should be safe.

Note that this comment only applies to Durable Functions and not to any direct consumers of this framework.

[jviau]

Do we need to do any version rev for this?

[davidmrdavid]

@jviau: Yeah, perhaps. I know for DF users this is a non-breaking change, but I struggle to determine if this is a major, minor, or patch release for DTFx users. After all, we're increasing a dependency by 2 major versions, and that seems significant. Thoughts, @jviau, @cgillum ?