Prepare MB future

- implement manifest filters to tweak manifests after they have been parsed
- make IEditorValidator public
- stop relying on InternalsVisibleTo Umbraco.ModelsBuilder

src/Umbraco.Core/Runtime/CoreInitialComposer.cs

@@ -58,7 +58,7 @@ namespace Umbraco.Core.Runtime
             composition.RegisterUnique<ManifestParser>();
 
             // register our predefined validators
-            composition.WithCollectionBuilder<ManifestValueValidatorCollectionBuilder>()
+            composition.ManifestValueValidators()
                 .Add<RequiredValidator>()
                 .Add<RegexValidator>()
                 .Add<DelimitedValueValidator>()
@@ -66,6 +66,9 @@ namespace Umbraco.Core.Runtime
                 .Add<IntegerValidator>()
                 .Add<DecimalValidator>();
 
+            // register the manifest filter collection builder (collection is empty by default)
+            composition.ManifestFilters();
+
             // properties and parameters derive from data editors
             composition.WithCollectionBuilder<DataEditorCollectionBuilder>()
                 .Add(() => composition.TypeLoader.GetDataEditors());