[cpp] Fix typing for abstracts

[vonagam]

When you use an abstract with an underlying type of typedef or an other abstract, typing skips resolving the underlying type itself jumping straight to resolving most concrete type instead.

Example why this problematic - if the underlying type is
Star<T>, Reference<T> or Struct<T>, the runtime C++ type end up being just T not T*, T& or cpp::Struct<T>:

@:structAccess
extern class Foo {
  @:native('new Foo')
  static function create(): cpp.Star<Foo>;
}

abstract Bar(cpp.Star<Foo>) from cpp.Star<Foo> {}

class Main5 {
  public static function main() {
    var bar: Bar = Foo.create();
  }
}

Cpp output:

::Foo bar = (*((new Foo())));

Don't know how to properly check resulted C++ runtime type in a test.

[Simn]

Could you add the failing example as a test?

[vonagam]

Yeah, but it will pass with or without this change, since in both cases cpp output will be valid, just not what you want, so it will be not really a test...

[vonagam]

Had an idea for the minimal test, found other potential bug:

var int: Int = 0;
var foo: cpp.Reference<Int> = int;
int += 1;
eq(foo, 1);

With -D analyzer-optimize produces cpp (cpp.Reference has @:semantics(reference), don't know if it is intended to help with such cases) (without analyzer-optimize it works ok):

this->eq(0,1,...)

[vonagam]

Added proper test.