Introduce DeclaratorDecl and pass DeclaratorInfo through the Decl/Sema interfaces.

Introduce DeclaratorDecl and pass DeclaratorInfo through the Decl/Sema interfaces.

DeclaratorDecl contains a DeclaratorInfo* to keep type source info.
Subclasses of DeclaratorDecl are FieldDecl, FunctionDecl, and VarDecl.
EnumConstantDecl still inherits from ValueDecl since it has no need for DeclaratorInfo.

Decl/Sema interfaces accept a DeclaratorInfo as parameter but no DeclaratorInfo is created yet.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@79392 91177308-0d34-0410-b5e6-96231b3b80d8