Interactivity API: Include preact/debug when WP_DEVELOPMENT_MODE is enabled.

[t-hamano]

What problem does this address?

When I attended a developer hours regarding the Interactivity API, I saw a participant ask if they had access to developer tools for debugging.

What is your proposed solution?

I temporarily made the following changes and was able to confirm that Preact Devtools worked on the front end.

diff --git a/packages/interactivity/src/init.js b/packages/interactivity/src/init.js
index fb510a9c00..79df6745d0 100644
--- a/packages/interactivity/src/init.js
+++ b/packages/interactivity/src/init.js
@@ -1,6 +1,7 @@
 /**
  * External dependencies
  */
+import 'preact/debug';
 import { hydrate } from 'preact';
 /**
  * Internal dependencies

Perhaps we need to detect whether a project is in development mode or not, but I think this tool will be useful to developers.

[cbravobernal]

Yep. But we will still need to make extra adjustments. At least, we should name the Directives component with each directive, so that way we don't have a huge list of Directives component 😅