* Fix the display of dimension units in the properties dialog. It was
previously not showing automatic units in the dialog.
* When placing dimension items (e.g. from paste or append), update the
units to the board units when the dimension uses automatic units.
Fixes https://gitlab.com/kicad/code/kicad/issues/6267
This is a board file format change to account for the new properties.
Also, we now only store the critical information about the dimension's
geometry in the board, rather than storing every drawn line.
The DIMENSION object is now an abstract base, and ALIGNED_DIMENSION
is the implementation that exists today (we will add more dimension
types in the future)