Registers an EditorToolContext as either a global context or a Component context for a specific target type.
A Global tool context is always available in the toolbar menu. A Component tool context is only available when the current selection contains a matching target type.
| EditorToolContextAttribute | Registers an EditorToolContext as either a global tool context or a Component tool context. |
| displayName | The name that displays in menus. |
| targetContext | If provided, the EditorTool will only be made available when the ToolManager.activeContextType is equal to targetContext. |
| targetType | Set to the type that this EditorTool or EditorToolContext can edit. Set to null if the tool is not specific to a Component and should be available at any time. |