Include XML doc metadata in generated shapes

[eiriktsarpalis]

Including XML documentation in generated shapes would provide important context for apps, especially AI powered ones. Since extracting XML docs at runtime can be unreliable, using the source generator to do this at compile time could be particularly helpful.

The obvious risk with such a change is inflated application sizes, so we might want to make this either opt in or only work for method shapes.

@AArnott thoughts?

[AArnott]

I can't think of a use case for this. And I share the concern about app size.

[eiriktsarpalis]

MCP customers have asked for this, I presume there exist other RPC scenarios that would be useful.

[AArnott]

I suppose if developing an MCP server, where descriptions of MCP tools is useful, xml doc comments might be used instead of the [Description] attribute. Is that what they're going for?
I hope this can be opt-in rather than tied to method inclusion.