Replace Less with CSS (#23508)

Backport https://github.com/go-gitea/gitea/pull/23481,
https://github.com/go-gitea/gitea/pull/23504 and
https://github.com/go-gitea/gitea/pull/23520 to 1.19, just so we have an
easier time with future backports.

Seems to work on a basic level. There was a merge conflict in
`RepoActionView.vue`, otherwise it merged cleanly.

---------

Co-authored-by: John Olheiser <john.olheiser@gmail.com>
Co-authored-by: Lauris BH <lauris@nix.lv>

package.json

@@ -28,11 +28,9 @@
     "jquery": "3.6.3",
     "jquery.are-you-sure": "1.9.0",
     "katex": "0.16.4",
-    "less": "4.1.3",
-    "less-loader": "11.1.0",
     "license-checker-webpack-plugin": "0.2.1",
     "mermaid": "10.0.2",
-    "mini-css-extract-plugin": "2.7.2",
+    "mini-css-extract-plugin": "2.7.4",
     "monaco-editor": "0.34.1",
     "monaco-editor-webpack-plugin": "7.0.1",
     "pretty-ms": "8.0.0",
@@ -45,7 +43,7 @@
     "vue-bar-graph": "2.0.0",
     "vue-loader": "17.0.1",
     "vue3-calendar-heatmap": "2.0.0",
-    "webpack": "5.76.0",
+    "webpack": "5.76.2",
     "webpack-cli": "5.0.1",
     "workbox-routing": "6.5.4",
     "workbox-strategies": "6.5.4",
@@ -64,7 +62,6 @@
     "eslint-plugin-vue": "9.9.0",
     "jsdom": "21.0.0",
     "markdownlint-cli": "0.33.0",
-    "postcss-less": "6.0.0",
     "stylelint": "15.2.0",
     "stylelint-declaration-strict-value": "1.9.2",
     "svgo": "3.0.2",