Add a jQuery style selection method
Right now it’s pretty inefficient to find all the text layers in a page. We already have an efficient method to find a layer by its name but rather than stopping at adding specific methods for each use case, I’d rather think of a more generic solution.

So something like a jQuery method makes sense to me:
```js
// returns an array of text layers in the selected document
sketch.$(`${sketch.Types.Text}`)

// returns all the layers in the page
sketch.$(‘*’, page)

// returns an array of layers whose name contains “special-name”
sketch.$(`[name*="special-name"]`)

// shortcut for the id
sketch.$(`#${id}`, page)

// shortcut for boolean properties
sketch.$(`:locked`)
sketch.$(`:not-locked`)
```

That selector string will need to parsed and translated to an NSPredicate for the search to be efficient.