Fixes https://github.com/octobercms/october/pull/2663
Adding to build 420+ because this might cause some issues, although it shouldn't. Hoping we don't ever have to roll this back because it fixes another inconsistency when using the model `filterFields` method... some will change values via $field->value (field accessor) and others will change via $this->value ($model accessor). This now puts the field accessor at a consistent priority (first) while retaining the fallback to model.
edcd899a79