[lldb] Make CompilerDecl::GetName (always) return template args (#116068)

I ran into this while look at a different bug (patch coming soon). This
function has only two callers. The first is SBTypeStaticField::GetName
(which doesn't care about templates), and the other is
CompilerDecl::GetCompilerContext (in the TypeQuery constructor), which
does want template arguments.

This function was (normally) returning the name without template args.
Since this code is only used when looking up a type in another shared
library, the odds of running into this bug are relatively low, but I add
a test to demonstrate the scenario and the fix for it nonetheless.

Amazingly (and scarily), this test actually passes without this change
in the default configuration -- and only fails with
-gsimple-template-names. The reason for that is that in the
non-simplified case we create a regular CXXRecordDecl whose name is
"bar<int>" (instead of a template record "foo" with an argument of
"int"). When evaluating the expression, we are somehow able to replace
this with a proper template specialization decl.