Added serializing object property to JSON

[svick]

Related to dotnet/corefx#41753 and https://github.com/dotnet/corefx/issues/41638.

This is a case where System.Text.Json currently has a performance issue, so I think it makes sense to add a benchmark for it, independently of whether the PR dotnet/corefx#41753 is accepted into corefx.

[adamsitnik]

LGTM, thank you!

[ahsonkhan]

Thanks!

[ahsonkhan]

With your fix from https://github.com/dotnet/corefx/issues/41638, is the performance of SerializeToString and SerializeObjectProperty almost identical now or is there still some gap here?

[adamsitnik]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[billwert]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[svick]

@ahsonkhan There is still some gap, though considering that SerializeObjectProperty does more, I'd say it's fairly small. For example, for the Dictionary<string, string> case, SerializeToString takes ~44 us, while SerializeObjectProperty takes now ~51 us (for comparison, previously it was over 2200 us).

But I haven't looked further into it, so it's possible there are still other optimizations to be had.