Add knip linter (#36442)

This adds [knip](https://github.com/webpro-nl/knip), a tool to find
unused files, dependencies and exports in JS. Fixed all discovered
issues.

1. knip apparently has some issue resolving imports from `d.ts` to `.ts`
so I worked around it by moving the two affected types to where they are
used.
2. I don't know why `modules/fomantic/dropdown.ts` had a new typescript
error, but I fixed it.
3. Use named export for `EsbuildPlugin`, I think this was added
recently.

web_src/js/globals.d.ts

@@ -49,7 +49,26 @@ interface Element {
 }
 
 interface Window {
-  config: import('./web_src/js/types.ts').Config;
+  config: {
+    appUrl: string,
+    appSubUrl: string,
+    assetVersionEncoded: string,
+    assetUrlPrefix: string,
+    runModeIsProd: boolean,
+    customEmojis: Record<string, string>,
+    pageData: Record<string, any>,
+    notificationSettings: Record<string, any>,
+    enableTimeTracking: boolean,
+    mentionValues: Array<{
+      key: string,
+      value: string,
+      name: string,
+      fullname: string,
+      avatar: string,
+    }>,
+    mermaidMaxSourceCharacters: number,
+    i18n: Record<string, string>,
+  },
   $: typeof import('@types/jquery'),
   jQuery: typeof import('@types/jquery'),
   htmx: typeof import('htmx.org').default,