Remember to instantiate explicit template argument lists in a friend

Remember to instantiate explicit template argument lists in a friend
function declaration.

We'd previously often just drop these on the floor, and friend
redeclaration matching would usually (but not always) figure out the
right redeclaration anyway.

Also, don't try to match a dependent friend function template
specialization to a template until instantiation, and don't forget to
reject qualified friend declarations in dependent contexts that don't
name an already-declared entity.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@350915 91177308-0d34-0410-b5e6-96231b3b80d8