Support in hasDeclaration for types with getDecl()

    
Using a new metafunction for detecting the presence of the member
'getDecl' in a type T, added support to hasDeclaration for any such type
T. This allows hasDecl() to be replaced and enables several other
subclasses of clang::Type to use hasDeclaration.

Updated unittests and LibASTMatchersReference.html.

Reviewers: klimek
llvm-svn: 175532