Rename Selector::getName() to Selector::getAsString(), and add

a new NamedDecl::getAsString() method.

Change uses of Selector::getName() to just pass in a Selector 
where possible (e.g. to diagnostics) instead of going through
an std::string.

This also adds new formatters for objcinstance and objcclass
as described in the dox.

llvm-svn: 59933