chore: upgrade to eslint FlatConfig

Author: iOvergaard

.eslintignore

@@ -0,0 +1,67 @@
+import globals from 'globals';
+import pluginJs from '@eslint/js';
+import tseslint from 'typescript-eslint';
+import localRules from 'eslint-plugin-local-rules';
+import wcPlugin from 'eslint-plugin-wc';
+import litPlugin from 'eslint-plugin-lit';
+import eslintPluginPrettierRecommended from 'eslint-plugin-prettier/recommended';
+
+import { includeIgnoreFile } from '@eslint/compat';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+const gitignorePath = path.resolve(__dirname, '.gitignore');
+
+export default [
+  // Recommended config applied to all files
+  pluginJs.configs.recommended,
+  ...tseslint.configs.recommended,
+  wcPlugin.configs['flat/recommended'],
+  litPlugin.configs['flat/recommended'],
+  localRules.configs['all-warn'],
+  eslintPluginPrettierRecommended,
+
+  // Global ignores
+  includeIgnoreFile(gitignorePath),
+  {
+    ignores: ['**/*.{cjs,mjs,js}', 'vite.config.ts', 'stories/'],
+  },
+
+  // Global config
+  {
+    plugins: {
+      'local-rules': localRules,
+    },
+    languageOptions: {
+      parserOptions: {
+        project: './tsconfig.json',
+        tsconfigRootDir: './',
+      },
+      globals: globals.browser,
+    },
+    rules: {
+      semi: ['warn', 'always'],
+      'no-unused-vars': 'off', //Let '@typescript-eslint/no-unused-vars' catch the errors to allow unused function parameters (ex: in interfaces)
+      'no-var': 'error',
+      '@typescript-eslint/explicit-module-boundary-types': 'off',
+      '@typescript-eslint/no-non-null-assertion': 'off',
+      '@typescript-eslint/no-explicit-any': 'off',
+      '@typescript-eslint/no-inferrable-types': 'off',
+      '@typescript-eslint/ban-ts-comment': 'off', //TODO: Remove (maybe)
+      '@typescript-eslint/ban-types': 'off', //TODO: Remove (maybe)
+      'lit/no-useless-template-literals': 'error',
+      'lit/prefer-nothing': 'error',
+      'no-restricted-syntax': [
+        'warn',
+        {
+          message:
+            'Elements should not be defined with customElement, use defineElement instead.',
+          selector:
+            'ClassDeclaration > Decorator[expression.callee.name="customElement"]',
+        },
+      ],
+    },
+  },
+];