Modified the expression parser's class wrapper to
support reporting "this" as a templated class.  The
expression parser wraps expressions in C++ methods
as methods with the signature

$__lldb_class::$__lldb_expr(...)

and previously responded to clang's queries about
$__lldb_class with the type of *this.  This didn't
work if *this was a ClassTemplateSpecializationDecl
because ClassTemplateSpecializationDecls can't be
the result of simple name queries.

Instead what we do now is respond that $__lldb_class
is a typedef and that the target of the typedef is
the (potentially templated) type of *this.  That is
much more robust.

Thanks to John McCall for key insights.

<rdar://problem/10987183>