Typed `this` in JavaScript Object Literals

[mjbvz]

From microsoft/vscode#27693

TypeScript Version: 2.3.4

const obj = {
    prop: 2,

    method() {
        this.prop|
    }
}

#14141 added typing for this in object literals in certain cases. Should this also be applied in regular JavaScript for intellisense, perhaps in a less strict form? We currently do not return any suggestions for this.| in obj

[mhegazy]

referenced in #14617

[mhegazy]

we should enable the inference by default for .js files (similar to --noImplicitAny contingent inferences)

[n-peugnet]

ok, this is exactly what I wanted, so I think this indeed should also be applied in regular JavaScript.

[sandersn]

Fix is up at #17252