Give 'this' keyword suggestion the same `sortText` as class properties if inside a class

From https://github.com/Microsoft/vscode/issues/66868

TypeScript Version: 3.4.0-dev.20190220

Search Terms:

• suggestions
• completions
• sortText

Code
For the javascript:

class Foo {
    constructor() {
        this.prop = 1;
    }

    render() {
        th
    }
}

• Trigger intellisense after th in render

Expected behavior:
this should be the first suggestion in VS Code

Actual behavior:
render and then prop are the first suggestions

The root cause of this is that the suggestion for this has a sortText of "0" while the one for prop and render have a sortText of "1". This causes VS Code to sort prop and render before this

@amcasey @minestarks I'm not sure if the current sorting issue would also effect VS

Playground Link:

Related Issues:

Reproduce the completion ordering in the TypeScript language service using the class example and inspect the completion entries for this, prop, and render. Update the relevant completion behavior so this uses the same sortText as class properties, then add or update a regression test covering the example and verify the resulting ordering.