Tweak and re-organize ESLint config (#38369)

* Tweak and re-organize ESLint config

* merge individual configs to the root config
* enable more eslint-plugin-import rules
* lint markdown files

* Lint

scss/tests/jasmine.js

@@ -1,5 +1,3 @@
-/* eslint-env node */
-
 /* eslint-disable camelcase */
 
 'use strict'

scss/tests/sass-true/register.js

@@ -1,8 +1,7 @@
-/* eslint-env node */
-
 'use strict'
 
 const path = require('node:path')
+
 const runnerPath = path.join(__dirname, 'runner').replace(/\\/g, '/')
 
 require.extensions['.scss'] = (module, filename) => {

scss/tests/sass-true/runner.js

@@ -1,10 +1,8 @@
-/* eslint-env node */
-
 'use strict'
 
-const { runSass } = require('sass-true')
 const fs = require('node:fs')
 const path = require('node:path')
+const { runSass } = require('sass-true')
 
 module.exports = (filename, { describe, it }) => {
   const data = fs.readFileSync(filename, 'utf8')