Remove file-loader dependency (#15196)

- Upgrade webpack to 5.28 to enable publicPath option
- Use asset modules in place of deprecated file-loader

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Lauris BH <lauris@nix.lv>

package.json

@@ -22,7 +22,6 @@
     "easymde": "2.14.0",
     "escape-goat": "3.0.0",
     "fast-glob": "3.2.5",
-    "file-loader": "6.2.0",
     "font-awesome": "4.7.0",
     "jquery": "3.6.0",
     "jquery.are-you-sure": "1.9.0",
@@ -44,7 +43,7 @@
     "vue-calendar-heatmap": "0.8.4",
     "vue-loader": "15.9.6",
     "vue-template-compiler": "2.6.12",
-    "webpack": "5.27.1",
+    "webpack": "5.28.0",
     "webpack-cli": "4.5.0",
     "workbox-routing": "6.1.2",
     "workbox-strategies": "6.1.2",