Use System.Text.Json source generator

[TimHess]

https://devblogs.microsoft.com/dotnet/try-the-new-system-text-json-source-generator/

[TimHess]

There may be some maintenance difficulties with this idea, we need to do more research on the level of IDE support for this feature and whether perf gains are even significant. This might be one of those things that's better in theory than reality

[bart-vmware]

In .NET 9, the usage of source generators causes errors in code analyzers, which is explained at dotnet/roslyn#75483 (comment). To summarize: the experience currently is crippled, in an attempt to address performance issues during build.

[bart-vmware]

Reopened because #1652 incorrectly referenced this issue.