Inferred type parameter constraints

[ahejlsberg]

With this PR we infer constraints for infer X type parameters in conditional types in certain circumstances. Specifically, when an infer X type parameter declaration occurs as a type argument in a type reference, we infer the constraint of the corresponding type parameter as the constraint of X. For example:

type Foo<T extends string> = { foo: T };
type Bar<T extends string> = { bar: T };
type Barify<T> = T extends Foo<infer X> ? Bar<X> : T;

Here, because the infer X declaration occurs as a type argument for the T type parameter in Foo, and because T has a constraint of string, the inferred constraint for X is string. Therefore, X meets the constraint required by Bar<T>.

Fixes #21631.