Tied up a few loose ends to support deeply nested property groups.

Simplified the call back for MaterialTypeSourceData::EnumeratePropertyGroups while also providing more data.
Made the Material Inspector join nested property group display names to be like "Layer 1 | Base Color", since the leaf property groups are shown as a flat list in the inspector.
Fixed CreateMaterialAssetFromSourceData to include the imported json files in the list of sourceDependencies. This triggers the Material Editor to hot-reload when one of these json files changes.
Updated a few places that were still assuming only one level of property group.
Updated EditorMaterialComponentInspector to apply the per-property-group material functors, before it was still only applying the top-level onces.
Moved some accessor function implementations to the cpp files, per feedback on another already-merged PR.

Testing:
Made changes to MinimalMultilayerPbr (in AtomSampleViewer) to use nested property groups, and saw the correct behavior in the Material Editor's property inspector.
Used MaterialComponent's property inspector to edit a StandardPbr material instance. Confrimed that functors were correctly controlling property visibility by enabling and disabling things like emissive and clear coat.
Used MaterialComponent's property inspector to edit a MinimalMultilayerPbr material instance. Saw all the expected groups and properties show up. Confirmed that per-group functors were correctly controlling property visibility.
Used MaterialComponent's property inspector to export a material instance and confirmed the .material file included the expected properties.

Signed-off-by: santorac <55155825+santorac@users.noreply.github.com>

Gems/AtomLyIntegration/CommonFeatures/Code/Source/Material/EditorMaterialComponentUtil.cpp

@@ -151,9 +151,7 @@ namespace AZ
                             return true;
                         }
 
-                        // TODO: Support populating the Material Editor with nested property groups, not just the top level.
-                        AZStd::string_view groupName = propertyId.GetStringView().substr(0, propertyId.GetStringView().size() - propertyDefinition->GetName().size() - 1);
-                        exportData.SetPropertyValue(RPI::MaterialPropertyId{groupName, propertyDefinition->GetName()}, propertyValue);
+                        exportData.SetPropertyValue(propertyId, propertyValue);
                         return true;
                     });