Draft: paint, tools: Pick and paint a layer
Adds a paint option to 'Pick and Paint a Layer'. When active the layer under the brush is selected for painting, unless it is locked.
This stops the searching for which layer to select when painting, also bypassing a need to pick a layer.
Testing required, one design issue already apparent. Creating a new transparent layer to paint on, will not take paint, if there is something select-able below. However, if all your paint layers are established, this MR makes painting on multiple layers, a more natural process.
'Alt + middle mouse' also selects the layer beneath the cursor, modifier shortcut reassignments were a bit broken last I checked. However for tablet users it should be possible to reassign this modifier to something suitable. From memory, I found if conflicted with other alt-click usages just enough to cause inadvertent layer picking, and stopped using it. This might be just me though.