Use JSON source generator

[jnyrup]

With the switch to System.Text.Json in #85 we can further improve TimeZoneNames for NativeAOT applications by switching to a source generated TimeZoneData JSON deserializer.

Unfortunately System.Text.Json does not (yet) support init only properties, see https://github.com/dotnet/runtime/issues/58770. For this draft I went with public setters, but alternatively a parameterized constructor should also work.

When I ran DataBuilder the order of the output changed, which I guess is either due non-stable dictionary sorting or that the CurrentCulture on my machine is a mix of en-US/en-GB and da-DK (reported as en-DK).

I made a quick benchmark on calling TimeZoneData.Load() on .NET6 using Benchmarkdotnet which only focuses on the performance benefits of switching to a source generated JSON deserializer.	branch	Mean	Error	StdDev	Ratio
main	174.5 ms	2.98 ms	2.49 ms	1.00
PR	114.8 ms	2.25 ms	2.10 ms	0.66

Some stats on a TimeZoneNames.NativeAot application.

main:

• File size of TimeZoneNames.NativeAot.exe is 6091 KB
• Crashes at runtime with

  Unhandled Exception: System.TypeInitializationException: TypeInitialization_Type_NoTypeAvailable
  ---> System.NotSupportedException: DeserializeNoConstructor, JsonConstructorAttribute, TimeZoneNames.TimeZoneData Path: $ | LineNumber: 0 | BytePositionInLine: 1.
  ---> System.NotSupportedException: DeserializeNoConstructor, JsonConstructorAttribute, TimeZoneNames.TimeZoneData

PR:

• File size of TimeZoneNames.NativeAot.exe is 4420 KB
• Works at runtime.

[mattjohnsonpint]

Thanks!