common libs: Update symbol I/O for v8 file format
This MR updates the symbol IO for the v8 file format.
A small behavioral change that this MR adds is that the symbol I/O code now sorts the symbol's pins the same way KiCad proper does: alphabetically by pin "number" field, so e.g. "A1, A10, A11, A12, A2, A3, ... A9, B1, B10, B11, ..." for a 12-column BGA.
Edited by jaseg