BUG:335092 Switch to a tool appropriate to the layer type

On switching to a vector layer, if the current tool doesn't work on
vector layers, switch to the interaction tool, and on switching to a
pixel layer, if the current tool doesn't work on a pixel layer, switch
to the freehand brush.

It might be possible to do this more neatly by having different shape
activation id's, but that's a huge can of worms.