[clang-repl] Consider the scope spec in template lookups for deduction guides.

isDeductionGuideName looks up the underlying template and if the template name
is qualified we miss that qualification resulting in an error. This issue
resurfaced in clang-repl where we call isDeductionGuideName more often to
distinguish between if we had a statement or declaration.

This patch passes the CXXScopeSpec information down to LookupTemplateName to
make the lookup more precise.

Differential revision: https://reviews.llvm.org/D147319