Please add ability to access MemberBlockItemSyntax in ExtensionDeclSyntax

[LesMacDonnald]

Hello
I want to generate mock implementation from the protocol declarations, but within a large codebase, protocol lives in the public module but I only want to generate the mock within Test modules, to avoid leaking mock to the concrete implementations and bloat binary sizes. Please implement ability to do this using PeerMacro and putting it oven extension.