see #90562 for details.

Y01 I'd like to eliminate the TODO that is part of following change:
+            InstanceContent ic = new InstanceContent();
+            Lookup context = new AbstractLookup(ic);
+            ic.add(project);
+            ic.add(project.getLookup().lookup(ProjectAccessor.class));
+            ic.add(project.getLookup().lookup(AuxiliaryConfiguration.class));
+            //TODO replace with generic apis..
+            ic.add(ic);
+            
+            OptionListener listener = new OptionListener( project );
+            dialog = 
ProjectCustomizer.createCustomizerDialog(CUSTOMIZER_FOLDER_PATH, context, 
null, listener, null );

I really do not like the reuse of InstanceContent as an API. It was never 
meant to be an API - it is just a helper support class. The API is Lookup, the 
SPI (and support) is Lookups, ProxyLookup, AbstractLookup, 
AbstractLookup.Content, InstanceContent, etc. That is why I'd like to find 
another way how to share data among individual panels. 

Imho, having such API would potentially be useful everywhere, not just in 
freefrom friend API and that is why I'd like to propose following changes:
#1: allow a Category to have associated lookup - that means adding new factory 
method in the Category class. The lookup might or might not be used, depending 
on the usage of the Category.
#2: However is the Category is used from 
ProjectCustomizer.createCustomizerDialog, it would be guaranteed that the 
content of the lookup is going to be added to the lookup passed back to the 
ProjectCustomizer.CompositeCategoryProvider.createComponent's lookup.
Imho this is similar pattern used in Tools/Options where each panel can donate 
a context and gets context merged from all others back.