feat: add the plugin system to the project

The PR adds the plugin system proposed in adobe/aem-boilerplate#254.
It also updates a few lib-franklin.js methods that were missing, along with the blocks that are impacted, and the template loading is converted to the new system.

Test URLs:
- Before: https://main--moleculardevices--hlxsites.hlx.page/
- After: https://plugin-system--moleculardevices--hlxsites.hlx.page/

blocks/breadcrumbs/breadcrumbs-create.js

@@ -160,9 +160,7 @@ function getName(pageIndex, path, part, current) {
 }
 
 export default async function createBreadcrumbs(container) {
-  const breadCrumbsCSS = new Promise((resolve) => {
-    loadCSS('/blocks/breadcrumbs/breadcrumbs.css', (e) => resolve(e));
-  });
+  const breadCrumbsCSS = loadCSS('/blocks/breadcrumbs/breadcrumbs.css');
 
   const path = window.location.pathname;
   const pathSplit = skipParts(path.split('/'));

blocks/card/card.js

@@ -163,15 +163,11 @@ class Card {
   }
 
   async loadCSSFiles() {
-    let defaultCSSPromise;
+    let defaultCSSPromise = Promise.resolve();
     if (Array.isArray(this.cssFiles) && this.cssFiles.length > 0) {
-      defaultCSSPromise = new Promise((resolve) => {
-        this.cssFiles.forEach((cssFile) => {
-          loadCSS(cssFile, (e) => resolve(e));
-        });
-      });
+      defaultCSSPromise = Promise.all(this.cssFiles.map(loadCSS));
     }
-    this.cssFiles && (await defaultCSSPromise);
+    return defaultCSSPromise;
   }
 }
 

blocks/carousel/carousel.js

@@ -397,11 +397,7 @@ class Carousel {
     let defaultCSSPromise;
     if (Array.isArray(this.cssFiles) && this.cssFiles.length > 0) {
       // add default carousel classes to apply default CSS
-      defaultCSSPromise = new Promise((resolve) => {
-        this.cssFiles.forEach((cssFile) => {
-          loadCSS(cssFile, (e) => resolve(e));
-        });
-      });
+      defaultCSSPromise = Promise.all(this.cssFiles.map(loadCSS));
       this.block.parentElement.classList.add('carousel-wrapper');
       this.block.classList.add('carousel');
     }