Introduce DeclaratorInfo and TypeLoc, intended to be used for storing and...

Introduce DeclaratorInfo and TypeLoc, intended to be used for storing and reading source information for types.

DeclaratorInfo will contain a flat memory block for source information about a type that came out of a declarator.
TypeLoc and its subclasses will be used by clients as wrappers to "traverse" the memory block and read the information.

Both DeclaratorInfo and TypeLoc are not utilized in this commit.

llvm-svn: 79391