Add "align stamps" option to Stamp Brush

When using a multi-tile stamp and painting with it by dragging the stamp, Tiled creates a "smudged" look, where the next stamp paint over the tiles of the previous stamp. This is usually not desirable behaviour, as it doesn't help with making an arc or filling a space with the stamp.

I'd like to see an option that forces the stamps to be aligned based on the bounding box of the stamp, similar to what you get when Filling with a stamp, but aligned to wherever you first start painting.

Comparison of the two options, current above, proposed below:

When using line mode (Shift+drag with the Stamp Tool), the resulting stamps don't overlap, but making complex shapes with this is tedious, and if you want the stamps to be grid-aligned, you have to be very careful with the slopes of the lines, which gets more difficult the larger the stamp is.

This aligned mode would be useful for painting arrangements of props and metatile-like features within maps that are otherwise created with subtiles directly. There are also many tilesets that have "terrains" that have multi-tile-long sides which can't be handled well with Terrains, and which are difficult to paint even with Automapping because one has to manually make sure the middles of the terrains are aligned correctly, and this feature would alleviate that.