[release/6.0] Remove redundant allocations from JsonSerializerOptions.GetConverter calls

[eiriktsarpalis]

Fixes Issue #65770, cherry-picks the fix from #65863.

Customer Impact

Fixes a customer reported issue. Currently every call to JsonSerializerOptions.GetConverter will force recreation of the default converters global state, which can substantially impact the allocation profile for custom converters that dynamically look up other converters. This is a regression from .NET 5.

Diff without whitespace

Testing

N/A

Risk

Low. Brings back a trivial check in the global state initialization method.

[ghost]

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Issue Details

---

Fixes Issue #65770, cherry-picks the fix from #65863.

Customer Impact

Fixes a customer reported issue. Currently every call to JsonSerializerOptions.GetConverter will force recreation the default converters global state, which can substantially impact the allocation profile for custom converters that dynamically look up other converters. This is a regression from .NET 5.

Testing

N/A

Risk

Low. Brings back a trivial check in the global state initialization method.

Author:	eiriktsarpalis
Assignees:	eiriktsarpalis
Labels:	area-System.Text.Json
Milestone:	-

[carlossanlop]

@eiriktsarpalis@steveharter@layomia just noticed this change affects an OOB package. Per the servicing instructions, if the csproj has the <IsPackable>true</IsPackable> property (which it does), then you also need to set the <GeneratePackageOnBuild>true</GeneratePackageOnBuild> property, and bump the <ServicingVersion>2</ServicingVersion> property to the next integer (3).

Here are a couple of examples (we had to add the property on the next release because we forgot): #65523#65733

Can one of you please add the change?

[eiriktsarpalis]

@carlossanlop done.

[ericstj]

Package change looks good.

[ericstj]

AOT failure is addressed in #66366. Linux_musl test failure is #56087