Option to render all tile layers in a group as a single layer.

Is your feature request related to a problem? Please describe.
I currently have an isometric grid. I find that I cannot vertically offset tiles without overlap issues. I can make a tileset with taller tiles, but this requires creating a custom image for each tile with a new offset.

Describe the solution you'd like
An option to group all layers within a group as rendering at the same time. Higher layers will render over lower layers ONLY if they have a tile on the same grid position. Otherwise it renders in whatever render order is set on the map.

For example, take this scene.

If you had a second layer with a y offset by -8 in this mode, you could render something like this, despite having all the same tiles.

Describe alternatives you've considered
There is no per tile render offset. There is also no way to offset the render offset in the tileset as far as I can find. I can create tiles that are taller or shorter, but these cause a great deal of copying. Additionally I can make maps using the object layer that can create this effect, however aligning these to a grid is very time consuming, and offsetting them in isometric requires changing both coordinates.

No files, tests, or entry points are named. Start by locating the tile-layer rendering path and existing group render-order behavior, then determine how the requested same-grid-position ordering interacts with isometric offsets. Done means grouped layers render together as described without changing unrelated map render order.