Ensure css_in_js file is created during dev

Once the vite server starts, we compile tailwind_all_the_way once in
order to generate the css_in_js file.

I cannot wait that we get rid of that file...

scripts/frontend/tailwindcss.mjs

 /* eslint-disable import/extensions */
+import { exec as execCB } from 'node:child_process';
 import path from 'node:path';
 import { fileURLToPath } from 'node:url';
+import util from 'node:util';
 import { createProcessor } from 'tailwindcss/lib/cli/build/plugin.js';
 
+const exec = util.promisify(execCB);
+
 // Note, in node > 21.2 we could replace the below with import.meta.dirname
 const ROOT_PATH = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '../../');
 
@@ -45,11 +49,27 @@ function wasScriptCalledDirectly() {
   return process.argv[1] === fileURLToPath(import.meta.url);
 }
 
+async function ensureCSSinJS() {
+  const cmd = 'yarn run pretailwindcss:build';
+  console.log('Ensuring config/helpers/tailwind/css_in_js.js exists');
+
+  const { stdout, error } = await exec(cmd, {
+    env: { ...process.env, REDIRECT_TO_STDOUT: 'true' },
+  });
+  if (error) {
+    throw error;
+  }
+
+  console.log(`'${cmd}' printed:`);
+  console.log(`${stdout}`);
+}
+
 export function viteTailwindCompilerPlugin({ shouldWatch = true }) {
   return {
     name: 'gitlab-tailwind-compiler',
     async configureServer() {
-      build({ shouldWatch });
+      await ensureCSSinJS();
+      return build({ shouldWatch });
     },
   };
 }
@@ -57,7 +77,8 @@ export function viteTailwindCompilerPlugin({ shouldWatch = true }) {
 export function webpackTailwindCompilerPlugin({ shouldWatch = true }) {
   return {
     async start() {
-      build({ shouldWatch });
+      await ensureCSSinJS();
+      return build({ shouldWatch });
     },
   };
 }