Property initialisation check in TS 3.5 is too strict for ember 3.5

[sandersn]

Start reading here: #29395 (comment)

import Component from '@ember/component';
import defaultTo from 'lodash/default-to';

export default class Welcome extends Component {
  greeting: string = defaultTo(this.greeting, "Hello");
}

Briefly, ember 3.5's Components have properties that are initialised by the base to a value, but Typescript doesn't know about this. Users should be able to squash the error by writing greeting!: string = ..., or by turning off strictPropertyInitialization, but can't today.

[kevinbarabash]

I've been experimenting with the idea of adding pragmas for each of the strict flags to enabling/disabling on a per file basis. The thinking was that there would be a new flag that disables strict checking of any type in .d.ts files and except for library definitions containing @strict-property-initialization (or other strict pragmas as needed). I think this could address the general problem of people wanting to use various strict flags with their code but not being able to because they break various libraries.