.d.ts export not properly handling recursive type bounds

[mor-n4]

Because the .d.ts export replaces wildcards by their explicit or implicit upper bound and does not yet have special handling for cycles, it can run into problems in case of recursive type bounds.

To reproduce (leads to invalid output):

class G0<T extends G0<T>> {}
let g0: G0<?>;

Leads to exception:

class G1<T extends G1<?>> {}

And similarly:

class A {}
class G2<T0 extends A,T1 extends G2<T0,?>> {}

Closely related, even this leads to invalid output (missing substitution):

class H<T> {}
class G3<T0, T1 extends H<T0>> {}
let g0: G3<string, ?>;

[mor-n4]

Note: an early experimental implementation is on branch postponed-GH-2241 (incomplete!).