[ASTImporter] Support importing FunctionTemplateDecl and CXXDependentScopeMemberExpr

* Also introduces ImportTemplateArgumentListInfo facility (A. Sidorin)

This re-commits r320942 after fixing the behaviour on '-fdelayed-template-parsing'
option and adding additional checks.

Patch by Peter Szecsi!

Differential Revision: https://reviews.llvm.org/D38692

llvm-svn: 321492