[lldb] Fix simple template names interaction with debug info declarations

Without checking template parameters, we would sometimes lookup the
wrong type definition for a type declaration because different
instantiations of the same template class had the same debug info name.

The added GetForwardDeclarationDIETemplateParams() shouldn't need a
cache because we'll cache the results of the declaration -> definition
lookup anyway. (DWARFASTParserClang::ParseStructureLikeDIE()
is_forward_declaration branch)

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D138834