"Did you forget to call 'X'?" for assignability errors

[DanielRosenwasser]

Discussed at #25306

We noticed a relatively high-occurring instance of an error:

Type X is not assignable to type () => X.
Type () => X is not assignable to type X.

Similarly, you can find users reporting issues on

Type Date is not assignable to type DateConstructor.
Type DateConstructor is not assignable to type Date.

We should see if the user forgot to call (or construct) one of the respective types if we can pull apart the context.