Terrain/mbalfour/terrain macro material component (#4500)

* Initial TerrainMacroMaterial Component.
The APIs will likely need to be adjusted once it gets hooked up to the renderer.
It also would benefit from better UX to prevent users from selecting the wrong material types, but there are separate tickets for the Editor to add features to allow for that.

Signed-off-by: Mike Balfour <82224783+mbalfour-amzn@users.noreply.github.com>

* Addressed PR feedback.

Signed-off-by: Mike Balfour <82224783+mbalfour-amzn@users.noreply.github.com>

* More PR feedback - add create/destroy notifications.

Signed-off-by: Mike Balfour <82224783+mbalfour-amzn@users.noreply.github.com>

Gems/Terrain/Code/Source/EditorTerrainModule.cpp

@@ -14,6 +14,7 @@
 #include <EditorComponents/EditorTerrainWorldComponent.h>
 #include <EditorComponents/EditorTerrainWorldDebuggerComponent.h>
 #include <EditorComponents/EditorTerrainWorldRendererComponent.h>
+#include <TerrainRenderer/EditorComponents/EditorTerrainMacroMaterialComponent.h>
 
 namespace Terrain
 {
@@ -24,6 +25,7 @@ namespace Terrain
             {
                 Terrain::EditorTerrainHeightGradientListComponent::CreateDescriptor(),
                 Terrain::EditorTerrainLayerSpawnerComponent::CreateDescriptor(),
+                Terrain::EditorTerrainMacroMaterialComponent::CreateDescriptor(),
                 Terrain::EditorTerrainSurfaceGradientListComponent::CreateDescriptor(),
                 Terrain::EditorTerrainSystemComponent::CreateDescriptor(),
                 Terrain::EditorTerrainWorldComponent::CreateDescriptor(),