Support definite assignment in TypesScript 2.7

[NN---]

Starting TypeScript 2.7 there is a special syntax for definite assignment.
https://blogs.msdn.microsoft.com/typescript/2018/01/17/announcing-typescript-2-7-rc/

TSLint should recognize this pattern and not issue error of noUninitialized.
In other words this should trigger this automatically: // tslint:disable-next-line no-uninitialized

class C {
    foo!: number;
}

From: palantir/tslint#3679

[alhugone]

The problem with definite assignment is that it again breaks strict-null-checks guarantees:

class C {
    foo!: number;
}

this code compiles despite that foo will be undefined. I see two options:

1. My rules are no loger needed - the compiler has this builtin check
   or/and
2. Don't use definite assignment.