[lldb] Prevent false positives with simple template names in SymbolFileDWARF::FindTypes

The provided test case was crashing because of confusion attempting to find types for `ns::Foo` under -gsimple-template-names. (This looks broken normally because it's attempting to find `ns::Foo` rather than `ns::Foo<T>`)

Looking up types can't give false positives, as opposed to looking up functions as mentioned in https://reviews.llvm.org/D137098.

Reviewed By: Michael137

Differential Revision: https://reviews.llvm.org/D140240