[Bug][http-client-csharp]: Inconsistency of `InputOperation.Summary` between emitter, mgc, autorest.csharp

[archerzz]

Describe the bug

• In the input json, we have defined Summary property: https://github.com/microsoft/typespec/blob/81f897739eed8b481d2e07de8fe9770ba9f44994/packages/http-client-csharp/emitter/src/type/input-operation.ts#L20
• However, it doesn't exist in the corresponding input type: https://github.com/microsoft/typespec/blob/81f897739eed8b481d2e07de8fe9770ba9f44994/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.Input/src/InputTypes/InputOperation.cs#L14
• It does exist in autorest.csharp: https://github.com/Azure/autorest.csharp/blob/0f630c2bf2f7116c3ebf212ce245a75c92d53f16/src/AutoRest.CSharp/Common/Input/InputTypes/InputOperation.cs#L18
• And more in autorest.csharp, we'll always set the Description if it's not available: https://github.com/Azure/autorest.csharp/blob/27aa096093e4e2efc4aa5c916eafd1c3df4ab48f/src/AutoRest.CSharp/Common/Input/InputTypes/Serialization/TypeSpecInputOperationConverter.cs#L85-L89

Reproduction

Check this PR which I tried to adopt TCGC properties regarding operation docs: https://github.com/microsoft/typespec/pull/4158 The root cause is that after adopting TCGC properties, the meaningful doc value is saved in Summary, instead of Description. And the Description is set to the operation name.

Questions

• Where do we want to determine the final document properties (e.g. Summary (for <summary>) and Description (for <remarks>)? In TCGC, or in emitter, or in our generator?
• Does MGC support Summary?

Checklist

• [X] Follow our Code of Conduct
• [X] Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
• [X] Check that this is a concrete bug. For Q&A open a GitHub Discussion.
• [X] The provided reproduction is a minimal reproducible example of the bug.

[archerzz]

Per discussion,

• We lost Summary property for InputOperation in MGC, so we need to add it back.
• However, we might want to change the property names to align with TCGC, e.g.
  • Rename Summary to Description <= TCGC description
  • Rename Description to Details <= TCGC details
  • For autorest.csharp, let's do the conversion in TypeSpecInputOperationConverter so that we don't need to change the InputOperation in it
• Remove the logic to set Description if empty in autorest.csharp