Remove or internalize JSON.NET dependency in Cosmos Provider

[ajcvickers]

If this is not possible, then we should:

• Give feedback to the SDK team
• Raise this issue with respect to 3.0 shipping and come up with a plan

[AndriySvyryd]

We need to wait until JsonConverter(https://github.com/dotnet/corefx/issues/34372) is available to be able to implement CosmosJsonSerializer
Also see CosmosSystemTextJsonSerializer

[ajcvickers]

See also: Azure/azure-cosmos-dotnet-v3#37

[ajcvickers]

Confirmed that we don't need to do this for 3.0.

[AndriySvyryd]

Now this is blocked on writable DOM support: dotnet/runtime#29690