Misc JS linting and naming tweaks (#10652)

- lowercase all js filenames except Vue components
- enable new lint rules, mostly focused on shorter code
- autofix new lint violations
- apply misc transformations indexOf -> includes and onevent-> addEventListener

Co-authored-by: Antoine GIRARD <sapk@users.noreply.github.com>

web_src/js/features/dropzone.js

@@ -1,5 +1,5 @@
 export default async function createDropzone(el, opts) {
-  const [{ default: Dropzone }] = await Promise.all([
+  const [{default: Dropzone}] = await Promise.all([
     import(/* webpackChunkName: "dropzone" */'dropzone'),
     import(/* webpackChunkName: "dropzone" */'dropzone/dist/dropzone.css'),
   ]);