The illegal white space testing for reference and value (library editor
only) fields are adequate to ensure the user cannot enter invalid white
space characters. Leading and/or trailing white space should not be an
issue for field storage in the schematic file as they are quoted. Rather
than silently removing the leading and/or trailing white space which is
frowned upon, let the user fix it.
Fixes lp:1659526
https://bugs.launchpad.net/kicad/+bug/1659526
* Refactor edit one field dialogs to use validators and transfer data to and
from window functions.
* Add code to DIALOG_SHIM to handle validation and transfer functions since
the base dialog class code is not called by EndQuasiModal().
* Add custom validator class for filtering field text control characters.
* Add new field validator to edit schematic component dialog field text
control.
* Add new field validator to edit fields in library editor dialog field
text control.
* Make a few LIB_PART member functions const.