Add missing tooltips for Align Distribute dialog

As noted in issue #3585 (closed) the Object -> "Align and Distribute..." dialog was missing tooltips for several icon controls. This change adds tooltips for those controls to that dialog.

In the implementation of actions, tooltip texts have sometimes been moved from .ui files to or otherwise created only within action-related code and data structures, e.g. actions-object-align.cpp, actions-node-align.cpp

Tooltips are not yet handled in all the circumstances seen with dialogs and .ui files. We still need tooltips within dialog .ui files until these are fully handled by the newer code-resident action-related data structures.

The added tooltip texts were copied from the action-related data structures mentioned above. Thus they match the tooltip texts displayed by the newer action-related code. However, I have seen elsewhere that periods at end of tooltip texts have been thought to be unneeded.

Perhaps this change should instead remove the trailing periods from both the tooltips added here and the tooltips at the above code locations. Please let me know.

Related to #3585 (closed)