Refactor zoom for Cesium and Leaflet maps.

[na9da]

What this PR does

Fixes #6761

Changes:

• Refactor zoom code path by moving the implementation of zoom behaviour for Cesium and Leaflet maps to Cesium/Zooming.ts and Leaflet/Zooming.ts. We could use a similar pattern to refactor picking code path by separating it to Map/Leaflet/Picking.ts and Map/Cesium/Picking.ts.
• Separate code for 3D/2D zoom view computation from the actual zooming mechanism. We now have compute3dZoomView and compute2dZoomView functions that computes the zoom views for different target types. This makes it easier to understand and also improves extensibility without touching other parts of the code.
• Improved zooming to clamped DataSource entities:
  

  terriajs/lib/Map/Cesium/compute3dZoomView.ts

  Lines 239 to 250 in 0ba6212

  	if (boundingSphere && isAnyEntityClampedToGround) {
  	// When zooming to clamped entities from a far away point, because the high
  	// LOD terrain tiles have not yet been loaded, the computed bounding sphere
  	// will be inaccurate and the resulting zoom might be far off from where
  	// the entity is actually placed. To get a better focus on clamped
  	// entities, we sample the terrain in highest detail to precisely clamp the
  	// bounding sphere to the terrain before we zoom to it.
  	await preciselyClampBoundingSphereToGround(
  	boundingSphere,
  	cesium,
  	boundingSphere
  	);

  
  This replicates a similar change to the Cesium Viewer. And here is a before and after example. See how when zooming to the Ducky, in the before example it is nowhere to be seen.
• Add option to zoom to an array of MappableMixin.Instance types.
• More spec coverage

Test me

• Open this CI link and randomly test different types of items to see if they work as expected

Checklist

• There are unit tests to verify my changes are correct or unit tests aren't applicable (if so, write quick reason why unit tests don't exist)
• I've updated relevant documentation in doc/.
• I've updated CHANGES.md with what I changed.
• I've provided instructions in the PR description on how to test this PR.

[na9da]

The idealZoom behaviour has been folded into the rest of the zoom code path.

[na9da]

Instead of zooming to first mappable in the workbench, we zoom to a view showing all the mappables.

[nf-s]

This PR also fixes

• 3DTiles catalog items causing errors in 2D (Leaflet) mode #6303

[nf-s]

Looks great! This is so much cleaner than before. I just have two small comments

I tested with a bunch of catalog items and could only find one issue with this:

Improved zooming to clamped DataSource entities:
here is a before and after example. See how when zooming to the Ducky, in the before example it is nowhere to be seen.

This works for me in "3d terrain" mode, but in "3d smooth" mode I still get put under the globe. This may be out-of-scope for this PR, if so let me know and I can make a ticket

[nf-s]

Can you please type target here.

Also, can you please use ZoomTarget here

terriajs/lib/Models/NoViewer.ts

Lines 28 to 31 in bdb0b60

	doZoomTo(
	v: CameraView | Rectangle | MappableMixin.Instance,
	t: any
	): Promise<void> {

[nf-s]

I think keeping ZoomView3d flexible will might help us in the long run - as then it will be easier to implement zoom behaviour for new catalog items/mappable items.

But there is a trade off in therms of maintenance costs. What do you think?