fix(eslint): Improve the globs for JS files

* Explicitly match file extensions in all globs, thus preventing eslint from trying to run on unsupported file types.
  * Include the defaults: `.js`, `.mjs`, and `.cjs`
  * Include`.jsx`
  * Include `.mustache`, since there are a couple JS template files with that suffix.
* Fix some incorrect globs (`**.js` -> `**/*.js`) which were the source of some unexpected lint failures.

.eslintrc.cjs

@@ -1,22 +1,24 @@
-const mongoFiles = ['ansible/playbooks/files/migrate_data.{js,mjs,cjs}']
+const jsSuffixes = '{js,mjs,cjs,jsx}'
+
+const mongoFiles = [`ansible/playbooks/files/migrate_data.${jsSuffixes}`]
 const nodeFiles = [
-  '**/build.dflt.{js,mjs,cjs}',
+  `**/build.dflt.${jsSuffixes}`,
-  '**/build.{js,mjs,cjs}',
+  `**/build.${jsSuffixes}`,
-  '**/config/**',
+  `**/config/**/*.${jsSuffixes}`,
-  '**/prebuild.{js,mjs,cjs}',
+  `**/prebuild.${jsSuffixes}`,
-  '**/prebuild/**',
+  `**/prebuild/**/*.${jsSuffixes}`,
-  '**/scripts/**',
+  `**/scripts/**/*.${jsSuffixes}`,
-  'packages/new-design/lib/**',
+  `packages/new-design/lib/**/*.${jsSuffixes}`,
-  'sites/backend/**',
+  `sites/backend/**/*.${jsSuffixes}`,
-  'sites/*/mdx/**',
+  `sites/*/mdx/**/*.${jsSuffixes}`,
-  'sites/*/themes/**',
+  `sites/*/themes/**/*.${jsSuffixes}`,
 ]
 const frontendFiles = [
-  '**/components/**',
+  `**/components/**/*.${jsSuffixes}`,
-  '**/hooks/**',
+  `**/hooks/**/*.${jsSuffixes}`,
-  '**/pages/**',
+  `**/pages/**/*.${jsSuffixes}`,
-  '**/page-templates/**',
+  `**/page-templates/**/*.${jsSuffixes}`,
-  'packages/i18n/**/*.md/*.js',
+  `packages/i18n/**/*.md/*.${jsSuffixes}`,
 ]
 
 module.exports = {
@@ -64,7 +66,7 @@ module.exports = {
       },
     },
     {
-      files: ['**'],
+      files: [`**/*.${jsSuffixes}{,.mustache}`],
       excludedFiles: [].concat(mongoFiles, nodeFiles, frontendFiles),
       env: {
         'shared-node-browser': true,
@@ -81,7 +83,7 @@ module.exports = {
     },
     // Additional globals for JavaScript files that happen to contain Mocha tests
     {
-      files: ['**/tests/**', '**/*.test.mjs'],
+      files: [`**/tests/**/*.${jsSuffixes}`, `**/*.test.${jsSuffixes}`],
       env: {
         mocha: true,
       },
@@ -89,7 +91,7 @@ module.exports = {
 
     // JSON files
     {
-      files: ['*.json', '*.json5', '*.jsonc'],
+      files: ['**/*.{json,json5,jsonc}{,.mustache}'],
       extends: ['plugin:jsonc/recommended-with-jsonc'],
       parser: 'jsonc-eslint-parser',
     },