Improve completions for decorators

**Is your feature request related to a problem? Please describe.**

Completions when adding decorators could be improved. If I add a `@description` decorator today it completes to `@description()`, but since it only accepts strings it should complete to `@description('')`. Same goes for `@metadata` and `@allowed`, they are of type array and object and could be completed to `@metadata({})` and `@allowed([])`.

**Describe the solution you'd like**

I would like for it to to work like this.

```bicep
// Adding decorators today
@metadata()
@allowed()
@description()
param myParam string

// What I would like to get
@metadata({})
@allowed([])
@description('')
param myParam string
```