Skip the shadowing decl and instead reference the top-most shadowed decl
(ie. follow any shadowed decls up the chain).
Also fix `getShorthandShadows` missing references in `MemberDeclRefExpr`
by using `getReferencedDecl` instead of assuming it is a `DeclRefExpr`.
Resolves rdar://99730146, rdar://100006415, and rdar://103449038.