[diagnostic] Name suggest for override should only list virtual functions

[dlangBugzillaToGithub]

Adam D. Ruppe (@adamdruppe) reported this on 2019-08-23T13:40:19Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=20157

Description

Easier to describe in code:

---
class A {
        final void a(int) {}
        void a(string) {}
}
class B : A {
        override void a(int) {}
}
---

Yields:

Error: function bug.B.a cannot override final function bug.A.a
Error: function void bug.B.a(int) does not override any function, did you mean to override void bug.A.a(int)?


I didn't mean to override a(int) because it is final, the compiler error message could make sure it is at least suggesting a relevant virtual function.