Scripting: Signal for brush changing

[eishiya]

It is occasionally desirable to react to the current brush changing. For example, one may want to select a different layer based on the brush's contents, or sort the brush's tiles into multiple layers automatically. However, there is currently no signal for this, and listening to changes to tiled.mapEditor.currentBrush doesn't work because that TileMap gets replaced rather than modified when the brush changes.

So, I'd like to request something like tiled.mapEditor.brushChanged (or currentBrushChanged to match currentBrush).
Similarly to TileMap.regionEdited, this signal should probably not fire on changes resulting from scripts, to avoid infinite loops.

Somewhat related: There are also no signals for the tiles selected in a Tileset or in TilesetsView changing, those may also be useful occasionally. So far, the only scenarios where I've wanted the latter has been as a potential alternative to brushChanged, though.