[DX] Allow more granulated return type completion, to separate from closures and makes easier to review

[TomasVotruba]

We've done similar split in the past, to make type declaration level work in as small steps as possible. This would concert few ReturnType* rules that now handle all functions, method, closure together.

The closure rules should be split of these and have separate rule inside TypeDeclarationLevel

Ref https://x.com/apefm/status/1803148500693102681