[Issue 17379] Mangle voldemort types as if they are defined in the outer scope to avoid exponential symbol name length with templates

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17379

--- Comment #1 from Georgi D <georgid at outlook.com> ---
I discussed this is Andrey and Walter at D-Conf 2017 and the overall agreement
is that it makes sense to change the mangling of voldemort types this way.

For the example above the mangled name changes like this:

- _D4test10__T3fooTiZ3fooFNaNbNiNfiZS4test10__T3fooTiZ3fooFiZ6Result
+ _D4test10__T3fooTiZ3fooFNaNbNiNfiZS4test10__T3fooTiZ6Result

--