[TrailingObjects] Convert AST classes that had a ASTTemplateKWAndArgsInfo.

So, also:

- Moved the TemplateArgumentLoc array out of the
  ASTTemplateKWAndArgsInfo class (making it a simple fixed-size object),
  to avoid needing to have a variable-length object as part of a
  variable-length object. Now the objects that have a
  ASTTemplateKWAndArgsInfo also have some TemplateArgumentLoc objects
  appended directly.

- Removed some internal-use accessors which became simply a wrapper on
  getTrailingObjects.

- Moved MemberNameQualifier out of the MemberExpr class, renamed it
  MemberExprNameQualifier, because the template can't
  refer to a class nested within the class it's defining.

llvm-svn: 256570