Allow transforming selection in SelectionTool

[axelboc]

• I add a prop called transformSelection to SelectionTool, which allows transforming the selection before it gets passed to onSelectionChange, onSelectionEnd and the children render prop. This cleans up the code of AxialSelectionTool quite a bit, since we no longer have to monkey-patch those three props in order to turn the user's selection into an axial selection.
• I change the way AxialSelectionTool transforms the user's selection into an axial selection. Instead of doing data -> world -> data, we now just do world -> data. See comments.
• I move the dimension mapper's Axis type ('x' | 'y') into @h5web/shared so I can re-use it everywhere. The name technically conflicts with our Axis component, but it doesn't seem to be a problem for now.

[loichuder]

That's great 👍