Resolve ambiguous naming of 'layers' in TileSets

[snailrhymer]

Describe the project you are working on

Generic TileMap workflow, thinking particularly about new users' experiences (related to discussion on #1769).

Describe the problem or limitation you are having in your project

Currently, TileSet uses the terms 'Physics Layer', 'Occlusion Layer' etc. This is likely to cause confusion, particularly with new users. For example, a Physics Layer in this context specifies (in part) which Collision Layers a tile will belong to. Elsewhere, the layer that collision layer refers to here, is called a physics layer:

and likewise for the navigation layers:

It's easy to imagine many TileMap tutorials will state something along the lines of "you might think that Physics Layer means X, when really it means Y", which I think is a situation best avoided. It's true that once users have spent some time with these, they'll have a better understanding of what is actually going on. There's nevertheless the risk that users will either avoid using these very powerful tools because they find them unapproachable, or that they sink time into setting them up incorrectly because they've misunderstood the terminology.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Use different terminology to refer to these meta layers/layer groups. Unfortunately, I don't have any firm ideas on this front - proposals are welcomed below.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

Old name -> New name

If this enhancement will not be used often, can it be worked around with a few lines of script?

The workaround would be getting familiar with the systems, which arguably isn't a massive price to pay to use the systems. If it's possible to cut down on misunderstandings by renaming, that still seems preferable.

Is there a reason why this should be core and not an add-on in the asset library?

It's a key part of the TileMap workflow.

[snailrhymer]

'Physics Behaviour' feels like it might cover the collision layer, collision mask and physics material settings nicely, and a quick search doesn't reveal anything it clashes with.

[Mickeon]

4.3 completely deprecates TileMap (one or more layers) in favour of one or more TileMapLayer nodes, which is more inline with Godot's node hierarchy design. This by itself should reduce the confusion by a large margin.