Upgrade React Router to v6.x (#1099)

There are a whole bunch of changes here, but most revolve around converting small components to function components or wrapping more complex ones in function components, since v6 has embraced hooks wholesale, and there's not another way to do a lot of basic navigation stuff with classes now.

Part of #1082, obsoletes #1035.

Author: Mr0grog

package-lock.json

@@ -37,7 +37,7 @@
     "react": "^18.3.1",
     "react-aria-modal": "^5.0.2",
     "react-dom": "^18.3.1",
-    "react-router-dom": "^5.3.4",
+    "react-router-dom": "^6.30.1",
     "react-tooltip": "^5.29.1",
     "style-loader": "^4.0.0",
     "webpack": "^5.101.3",