Migrate to ESLint 9 with flat config

eslint.config.mjs

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+// @ts-check
+import stylistic from '@stylistic/eslint-plugin';
+import globals from 'globals';
+import tseslint from 'typescript-eslint';
+
+export default tseslint.config(
+	{
+		ignores: ['**/lib/**', '**/node_modules/**', 'build/**', 'samples/**'],
+	},
+	{
+		files: ['**/*.ts'],
+		languageOptions: {
+			globals: globals.node,
+			parser: tseslint.parser,
+		},
+		plugins: {
+			'@typescript-eslint': tseslint.plugin,
+			'@stylistic': stylistic,
+		},
+		rules: {
+			'@stylistic/semi': 'error',
+			'@stylistic/member-delimiter-style': ['error', {
+				multiline: { delimiter: 'semi', requireLast: true },
+				singleline: { delimiter: 'semi', requireLast: false },
+				multilineDetection: 'brackets',
+			}],
+			'indent': 'off',
+			'@stylistic/indent': ['warn', 'tab', { SwitchCase: 1 }],
+			'@typescript-eslint/no-floating-promises': 'error',
+			'no-extra-semi': 'warn',
+			'curly': 'warn',
+			'quotes': ['error', 'single', { allowTemplateLiterals: true }],
+			'eqeqeq': 'error',
+			'constructor-super': 'warn',
+			'prefer-const': ['warn', { destructuring: 'all' }],
+			'no-caller': 'warn',
+			'no-case-declarations': 'warn',
+			'no-debugger': 'warn',
+			'no-duplicate-case': 'warn',
+			'no-duplicate-imports': 'warn',
+			'no-eval': 'warn',
+			'no-async-promise-executor': 'warn',
+			'no-new-wrappers': 'warn',
+			'no-redeclare': 'off',
+			'no-sparse-arrays': 'warn',
+			'no-throw-literal': 'warn',
+			'no-unsafe-finally': 'warn',
+			'no-unused-labels': 'warn',
+			'no-restricted-globals': ['warn', 'name', 'length', 'event', 'closed', 'external', 'status', 'origin', 'orientation', 'context'],
+			'no-var': 'warn',
+			'@typescript-eslint/naming-convention': [
+				'warn',
+				{ selector: 'class', format: ['PascalCase'], leadingUnderscore: 'allow' },
+			],
+		},
+	}
+);

language-service/eslint.config.mjs

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+import rootConfig from '../eslint.config.mjs';
+import tseslint from 'typescript-eslint';
+import path from 'path';
+import { fileURLToPath } from 'url';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+
+export default tseslint.config(
+	...rootConfig,
+	{
+		languageOptions: {
+			parserOptions: {
+				projectService: {
+					defaultProject: path.join(__dirname, 'tsconfig.json'),
+				},
+			},
+		},
+	}
+);

lsif/eslint.config.mjs

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+import rootConfig from '../eslint.config.mjs';
+import tseslint from 'typescript-eslint';
+import path from 'path';
+import { fileURLToPath } from 'url';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+
+export default tseslint.config(
+	...rootConfig,
+	{
+		languageOptions: {
+			parserOptions: {
+				projectService: {
+					defaultProject: path.join(__dirname, 'tsconfig.json'),
+				},
+			},
+		},
+	}
+);

npm/eslint.config.mjs

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+import rootConfig from '../eslint.config.mjs';
+import tseslint from 'typescript-eslint';
+import path from 'path';
+import { fileURLToPath } from 'url';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+
+export default tseslint.config(
+	...rootConfig,
+	{
+		languageOptions: {
+			parserOptions: {
+				projectService: {
+					defaultProject: path.join(__dirname, 'tsconfig.json'),
+				},
+			},
+		},
+	}
+);