Fix select tool not selcting corner canvas pixels

[Zekiah-A]

Fixed the select tool as previously you were unable to drag select the last row of pixels on the X and Y axis

Before: Unable to select the very edge pixels ^

After: Now selects canvas edge pixel on x and y when mouse is dragged all the way to the edge

[Zekiah-A]

Also I am unsure why github displays so many commits for this PR, changes can be seen at "Files Changed"

[cameronwhite]

Good catch, thanks! I think there's also a similar issue in the mouse down handler, if you initially click below or to the right of the canvas

[Zekiah-A]

We may need to offset the dotted line border for the rectangle of the selection by -1px on the X and Y, as even though selection is now technically correct, because it is on the very edge of the image the dotted line there is hard to see

[cameronwhite]

Good point - I see in DocumentSelection.Draw() that it's being offset slightly, which is probably why the left / top is easy to see

[Zekiah-A]

Okay this is epic 😎 everything works now, pinta is now better than photoshop, affinity, paint.net and maybe even MS paint

[cameronwhite]

Nice, looks good to me with that 0.5 translation removed