[Types] Unable to extend ILocator, and addFilter is missing from Locator

#### What are you trying to achieve?

I would like to extend the `ILocator` type in order to add a custom Locator to it (e.g. {da: string}) for selecting elements with a custom `data-automation` attribute.

I would also like to call `locator.addFillter()` without getting a TS error.

#### What do you get instead?

##### ILocator

I am unable to extend ILocator type as it isn't exported on the types:


##### Locator

I have to extend `Locator` to declare `addFilter`, as this property is missing from the generated types.

``` ts

interface Locator {
addFilter: (
callback: (
providedLocator: Record,
locatorObj: { type: string; value: string },
) => void,
) => void;
}

```

otherwise, I'll get this:

### Details

* CodeceptJS version: 2.6.8
* NodeJS Version: 12
* Operating System: OSX
* playwright: 1.3.0