This class aims to implement Design Token idea into FreeCAD themes. It
allows themes to use generic variables with generic values so we could
use one qss theme and change the style based on values from preference
packs.
The PR refactors FindPreferencePacksInPackage() and splits program logic from exception handling. It also handles std::exception to give more
information about a possible failure
This commit adds "<mod>/overlay" path to search paths of "overlay"
prefix. This allows preference packs to register custom overlay
stylesheets.
Fixes: #11023
Just changing the preference for hiding or showing a dock window does
not actually trigger a state change. To enable that, the preferences
pack manager must manually instruct the DockWindowManager to save its
state into the preferences before storing a preference pack, and must
instruct the DockWindowManager to load its new state from the
preferences after loading a pack.
Preference Packs are collections of preferences that can be applied en
mass to the user's current setup. Any preference that can be stored in
user.cfg can be stored in a preference pack, and they are designed to be
easy to distribute.
Support is also added for saving a subset of current preferences into a
new preference pack in order to facilitate easy creation of new
"themes", etc.
