[Proposal]: `params in` parameters

[333fred]

params in parameters

• Specification: TBD
• Discussion: [Proposal]: `params in` parameters #9118

Summary

It should be possible for params parameters to also be in.

Design meetings

• https://github.com/dotnet/csharplang/blob/main/meetings/2024/LDM-2024-09-06.md#params-in-parameters