perf(core): replace lazysizes with browser-level lazy loading (#1267)

_javascript/modules/plugins.js

@@ -1,6 +1,6 @@
 export { categoryCollapse } from './components/category-collapse';
 export { initClipboard } from './components/clipboard';
-export { imgLazy } from './components/img-lazyload';
+export { loadImg } from './components/img-loading';
 export { imgPopup } from './components/img-popup';
 export { initLocaleDatetime } from './components/locale-datetime';
 export { toc } from './components/toc';