Fix source generation support for tuples with explicitly named elements

[eiriktsarpalis]

When querying a ValueTuple type symbol for fields, the returned symbols include any explicitly named tupled elements. These do not correspond to runtime properties and as such should be filtered from the generated code.

Note that while the source generator could take advantage of this compile-time metadata, emitting serialization code that accounts for explicitly named tuple elements would diverge from the reflection-based behaviour. As such, all tuples will be serialized as { "Item1" : 1, "Item2" : 2 , ... } regardless of any element labels used at compile time.

Should be backported to release/6.0.

Fixes#58137.

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Issue Details

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When querying a ValueTuple type symbol for fields, the returned symbols include any explicitly named tupled elements. These do not correspond to runtime properties and as such should be filtered from the generated code.

Note that while the source generator could take advantage of this compile-time metadata, emitting serialization code that accounts for explicitly named tuple elements would diverge from the reflection-based behaviour. As such, all tuples will be serialized as { "Item1" : 1, "Item2" : 2 , ... } regardless of any element labels used at compile time.

Should be backported to release/6.0.

Fixes #58137.

Author:	eiriktsarpalis
Assignees:	eiriktsarpalis
Labels:	area-System.Text.Json
Milestone:	6.0.0

[eiriktsarpalis]

/backport to release/6.0

[github-actions]

Started backporting to release/6.0: https://github.com/dotnet/runtime/actions/runs/1205881963