Type definition changed on ImageManager v3.11

More a question than and issue.

Member `images` on `ImageManager` renamed to `_images` from [v3.11.0-beta.1](https://github.com/mapbox/mapbox-gl-js/tree/v3.11.0-beta.1).

Is this a member not meant to be used ?

I use this member to get the images of a current style before changing to another base map style so I can add them to the new selected style (as well as sources and layers) and keep the context the user is working with.

> This is a breaking change from 3.10 to 3.11 on the `ImageManager` class definition and breaks code using the `images` property.

_Originally posted by @polkduran in [f31af6e](https://github.com/mapbox/mapbox-gl-js/commit/f31af6eb1b7c46f8647af2cb35143385b1770fb3#r154747910)_

Start by comparing the ImageManager `images` member with its `_images` replacement in the v3.11.0-beta.1 changes. Determine whether the member is intended for public use and identify the supported way to preserve images across style changes; the issue is complete when the breaking-change question has a documented or implemented resolution.

Written by the indexing model from the issue text.