Rip out TemplateIdRefExpr and make UnresolvedLookupExpr and

Rip out TemplateIdRefExpr and make UnresolvedLookupExpr and
DependentScopeDeclRefExpr support storing templateids.  Unite the common
code paths between ActOnDeclarationNameExpr and ActOnTemplateIdExpr.

This gets us to a point where we don't need to store function templates in
the AST using TemplateNames, which is critical to ripping out OverloadedFunction.

Also resolves a few FIXMEs.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@89785 91177308-0d34-0410-b5e6-96231b3b80d8