Convert frontend code to typescript (#31559)

None of the frontend js/ts files was touched besides these two commands
(edit: no longer true, I touched one file in
61105d0618
because of a deprecation that was not showing before the rename).

`tsc` currently reports 778 errors, so I have disabled it in CI as
planned.

Everything appears to work fine.

package.json

@@ -68,6 +68,16 @@
     "@stoplight/spectral-cli": "6.11.1",
     "@stylistic/eslint-plugin-js": "2.2.1",
     "@stylistic/stylelint-plugin": "2.1.2",
+    "@types/dropzone": "5.7.8",
+    "@types/jquery": "3.5.30",
+    "@types/katex": "0.16.7",
+    "@types/license-checker-webpack-plugin": "0.2.4",
+    "@types/pdfobject": "2.2.5",
+    "@types/sortablejs": "1.15.8",
+    "@types/swagger-ui-dist": "3.30.5",
+    "@types/throttle-debounce": "5.0.2",
+    "@types/tinycolor2": "1.4.6",
+    "@types/toastify-js": "1.12.3",
     "@typescript-eslint/eslint-plugin": "7.14.1",
     "@typescript-eslint/parser": "7.14.1",
     "@vitejs/plugin-vue": "5.0.5",