IDE Scripts can now read a selected method's parameters and return type

The Studio Scripting API's StudioSelectedMember exposes a selected method's Name, Kind, and source Range, but not its parameter list or return type. IDE Scripts that want to generate documentation headers, wrappers, or call sites must currently parse source text themselves, which is fragile and not an appropriate public solution.

This change adds a structured StudioParameter type and read-only Parameters and ReturnType members to StudioSelectedMember, so scripts can read the full declared method shape directly.