Background and context:
1. Instagram by default requires you to be logged in.
2. Your account can LIKE posts.
3. Getting all of your likes from IG can be a pain.
As an active IG user, I want to be able to download only posts I've liked.
The information of whether or not your logged-in user has liked the target post is available in the API results, but was not available to the end-user for filtering.
This small change allows `user_has_liked` to be used to e.g. download only liked posts of an entire IG account.
Example use:
```
$ gallery-dl --cookies-from-browser FIREFOX--filter 'user_has_liked' https://www.instagram.com/imgur/
```
This will only download the posts that have `has_liked: True` set in the returned REST API data.
Note: it will still need to loop through the entire account's posts since this is done per-post basis instead of looping just the liked posts, but at least you are able to use this IG feature as a download marker.
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