Support to decorators in TypeScript

[lacolaco]

Motivation
I'd like to highlight my code relating Angular. Angular uses @Decorators often like below:

@Component({
  selector: 'my-app',
  template: `<div>Hello World!</div>`
})
export class AppComponent {}

A decorator is technically a function, but I want to separate its color from normal functions.

Currently, decorators are tokenized as function in language-typescript

Description

Adding .meta-like class to decorator name token.

[lacolaco]

In addition, an object in the decorator is not tokenized correctly. As the below image, template and changeDetection are property names but not tokenized.

[RunDevelopment]

With #2820, decorators will have a dedicated .decorator class.

an object in the decorator is not tokenized correctly

The syntax is too similar to type annotations. We will not able to distinguish between the two correctly. Sorry, but that isn't possible to implement with Prism.