[ci no changelog needed]
This is fixed copy of already reviewed #3384
[Task link](https://www.pivotaltracker.com/story/show/181413200)
This PR implements content clipping for the ScrollArea component.
List of changes:
- Implemented `InstanceWithAttachedLayer` abstraction that allows creating additional sublayers for our components. In the future, this abstraction can be used for text rendering as well (right now text rendering requires additional hardcoded layers).
- Fixed `complex-shape-system` demo scene by removing `node_searcher_mask` layer.
- Fixed `SublayersModel::remove` - it was not clearing the `layer_placement` hashmap.
- Implemented disabling the wheel scrolling in `Navigator`, and refactored it to reduce the number of functions arguments by introducing a `NavigatorSettings` struct.
Video (`scroll_area` demo):
https://user-images.githubusercontent.com/6566674/164506455-e177a7a7-9f1c-4f50-888f-112423cebbe4.mp4
# Important Notes
- `InstanceWithAttachedLayer` is implemented in such a way that it allows an extension in the future - namely to use it to simplify text rendering. The implementation might be simplified though.
In this PR two things are implemented:
1. Node Searcher zoom factor (and therefore its size) is fixed no matter how you move the main camera. The node searcher is also positioned directly below currently edited node at all times.
2. Node growth/shrink animation when you start/finish node editing. After animation end the edited node zoom factor is also fixed and matches the zoom factor of the node searcher.
See attached video with different ways of editing/creating nodes:
https://user-images.githubusercontent.com/6566674/157348758-2880aa2b-494d-46e6-8eee-a22be84081ed.mp4
#### Technical details
1. Added several additional scene layers for separate rendering: `node_searcher`, `node_searcher_text`, `edited_node`, `edited_node_text`. Searcher is always rendered by `node_searcher` camera, edited node moves between its usual layers and `edited_node` layer. Because text rendering uses different API, all node components were modified to support change of the layer.
2. Also added `node_searcher` DOM layer, because documentation is implemented as a DOM object.
3. Added two FRP endpoints for `ensogl::Animation`: `on_end` and `set_value`. These endpoints are useful while implementing growth/shrink animation.
4. Added FRP endpoints for the `Camera2d`: `position` and `zoom` outputs. This allows to synchronize cameras easily using FRP networks.
5. Growth/shrink animation implemented in GraphEditor by blending two animations, similar to Node Snapping implementation. However, shrinking animation is a bit tricky to implement correctly, as we must always return node back to the `main` scene layer after editing is done.
