Some changes to detangle some service and DSL objects when applying plugins:

- Added PluginAwareInternal to provide access to the PluginManager for a target object
- Use this in DefaultObjectConfigurationAction to apply plugins using a PluginManager, for `apply plugin: ...` DSL usages.
- Use this in DefaultPluginRequestApplicator to apply plugins using a PluginManager, for `plugins { ... }` DSL usage.