Support default parameter values in lambdas

• Proposed
• Prototype: No prototype needed
• Implementation: done
• Specification: https://github.com/dotnet/csharplang/blob/main/proposals/csharp-12.0/lambda-method-group-defaults.md

Design Discussions

• https://github.com/dotnet/csharplang/blob/main/meetings/2022/LDM-2022-04-27.md#default-parameter-values-in-lambdas
• https://github.com/dotnet/csharplang/blob/main/meetings/2022/LDM-2022-07-13.md#lambda-default-parameters
• https://github.com/dotnet/csharplang/blob/main/meetings/2022/LDM-2022-10-10.md#params-support-for-lambda-default-parameters
• https://github.com/dotnet/csharplang/blob/main/meetings/2022/LDM-2022-11-02.md#default-parameter-values-in-lambdas