[EXT] Add new property: model-allow-density-reduction (#8488)

This PR fixes the merge conflicts found in
mapbox/mapbox-gl-js#13433 which I couldn't
address directly there (I suppose due to branch protections on the
original reporter branch), adds a new render test to cover this
behaviour and marks `model-allow-density-reduction` as `experimental`.

All credit goes to @JoshuaJMoore who did the initial implementation

Closes [MAPS3D-2107](https://mapbox.atlassian.net/browse/MAPS3D-2107)
and [GLJS-1561](https://mapbox.atlassian.net/browse/GLJS-1561)

## Launch Checklist

- [ ] Make sure the PR title is descriptive and preferably reflects the
change from the user's perspective.
- [ ] Add additional detail and context in the PR description (with
screenshots/videos if there are visual changes).
 - [ ] Manually test the debug page.
- [ ] Write tests for all new functionality and make sure the CI checks
pass.
 - [ ] Document any changes to public APIs.
 - [ ] Post benchmark scores if the change could affect performance.
- [ ] Tag `@mapbox/map-design-team` `@mapbox/static-apis` if this PR
includes style spec API or visual changes.
- [ ] Tag `@mapbox/gl-native` if this PR includes shader changes or
needs a native port.
- [ ] Tag `@mapbox/gl-native` if this PR disables any test because it
also needs to be disabled on their side.
- [ ] Create a ticket for `gl-native` to groom in the [MAPSNAT JIRA
queue](https://mapbox.atlassian.net/jira/software/c/projects/MAPSNAT/list)
if this PR includes shader changes or features not present in the native
side or if it disables a test that's not disabled there.

--

> [!NOTE]
> This PR was imported from the public repo and closes:
mapbox/mapbox-gl-js#13595
> ```
> <public>Add new property: `model-allow-density-reduction` (h/t
@JoshuaJMoore) (public-13595)</public>
> ```

Author: Isaac Besora Vilardaga <isaac.besora@gmail.com>

cc @mapbox/gl-js

[MAPS3D-2107]:
https://mapbox.atlassian.net/browse/MAPS3D-2107?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ
[GLJS-1561]:
https://mapbox.atlassian.net/browse/GLJS-1561?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

cc @mapbox/maps-android
cc @mapbox/maps-ios

cc @mapbox/sdk-ci

---------

Co-authored-by: Isaac Besora Vilardaga <isaac.besora@gmail.com>
Co-authored-by: Changelog autocreator bot <actions@github.com>
GitOrigin-RevId: 64bb4e75904e023db952a4054f4a575a9628c196

Author: 3 people