[libclang, bindings]: add spelling location

 o) Add a 'Location' class that represents the four properties of a
    physical location

 o) Enhance 'SourceLocation' to provide 'expansion' and 'spelling'
    locations, maintaining backwards compatibility with existing code by
    forwarding the four properties to 'expansion'.

 o) Update the implementation to use 'clang_getExpansionLocation'
    instead of the deprecated 'clang_getInstantiationLocation', which
    has been present since 2011.

 o) Update the implementation of 'clang_getSpellingLocation' to actually
    obtain spelling location instead of file location.

llvm-svn: 316278