[Proposal]: ref readonly method parameters

[Sergio0694]

ref readonly method parameters

• [x] Proposed
• [x] Prototype: Done
• [x] Implementation: Done
• [ ] Specification: https://github.com/dotnet/csharplang/blob/main/proposals/csharp-12.0/ref-readonly-parameters.md

Note: this proposal is a follow up to numerous conversations over the years about how in arguments are implemented in C#, both here on GitHub and on Discord (with folks like @stephentoub, @jaredpar, @tannergooding, @AaronRobinsonMSFT). To give context and cite the last example, see https://github.com/dotnet/runtime/issues/67445. Opening this so we can properly review it and hopefully start making some progress.

See https://github.com/dotnet/csharplang/blob/main/proposals/csharp-12.0/ref-readonly-parameters.md

Design Meetings

• https://github.com/dotnet/csharplang/blob/main/meetings/2022/LDM-2022-04-25.md#ref-readonly-method-parameters
• https://github.com/dotnet/csharplang/blob/main/meetings/2022/LDM-2022-05-09.md#ref-readonly-parameters
• https://github.com/dotnet/csharplang/blob/main/meetings/2022/LDM-2022-05-11.md#ref-readonly-method-parameters

[soroshsabz]

related to #188