Refactor branch/tag selector to Vue SFC (#23421)

Follow #23394

There were many bad smells in old code. This PR only moves the code into
Vue SFC, doesn't touch the unrelated logic.

update: after
https://github.com/go-gitea/gitea/pull/23421/commits/5f23218c851e12132f538a404c946bbf6ff38e62
, there should be no usage of the vue-rumtime-compiler anymore
(hopefully), so I think this PR could close #19851

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

webpack.config.js

@@ -196,6 +196,10 @@ export default {
     ],
   },
   plugins: [
+    new webpack.DefinePlugin({
+      __VUE_OPTIONS_API__: true, // at the moment, many Vue components still use the Vue Options API
+      __VUE_PROD_DEVTOOLS__: false, // do not enable devtools support in production
+    }),
     new VueLoaderPlugin(),
     new MiniCssExtractPlugin({
       filename: 'css/[name].css',