Turn the Link class into a template abstracting over the link's argument and
return types, but provide default template arguments that keep the generic,
unsafe "void* in, sal_IntPtr out" behvior.  That way, individual uses of the
Link class can be updated over time.

All the related macros are duplicated with ..._TYPED counterparts, that
additionally take the RetType (except for LINK_TYPED, which manages to infer the
relevant types from the supplied Member).

(It would have been attractive to change the "untyped" LinkStubs from taking a
void* to a properly typed ArgType parameter, too, but that would cause
-fsanitize=function to flag uses of "untyped" Link::Call.)

Change-Id: I3b0140378bad99abbf240140ebb4a46a05d2d2f8