Alignment buttons for points in the Path tool control bar

When multiple anchors/handles are selected with the Path tool, we should have the control bar show the alignment buttons that the Select tool's control bar has:

This will make it easier to line up the selected points with one another. There will be edge cases when dealing with colinearity and the selection of different combinations of anchor and handle pairings.

Start by locating the Path tool control bar and the Select tool control bar, then compare how their alignment controls are represented. Define behavior for multiple selected anchors and handles, including the colinearity and mixed anchor/handle cases mentioned in the issue; the work is done when the Path tool exposes equivalent alignment buttons with those cases handled.

索引モデルが issue の本文から書いたものです。