Goto Implementation should suggest all subtypes

[dbaeumer]

Steps to reproduce:

interface Person {
}

class Teacher implements Person {
}

class SeniorTeacher extends Teacher {
}

Goto implementation on Person only lists Teacher. It should list SeniorTeacher as well.

[fuafa]

In the situation below (it is a fourslash test in TypeScript), trigger goto implementation at x.hello()

jetbrains team member considers hello is a method of SuperBar, so, NotBar.hello should be returned, while TypeScript said NotBar and Bar are not structurally equal, so NotBar.hello should not be returned. Do you accept jetbrains' approach? If so, I can submit a pr for this.