chore: migrate to ESLint 9 and flat config

Related to bpmn-io/internal-docs#1042

client/src/app/cached/WithCachedState.js

@@ -99,7 +99,6 @@ export default function(Comp) {
       } = this.props;
 
       const {
-        // eslint-disable-next-line
         __destroy,
         cached
       } = this.state;

client/src/shared/ui/DropdownButton.js

@@ -165,7 +165,7 @@ export default class DropdownButton extends PureComponent {
       items,
       children,
       onClick,
-      closeOnClick, // eslint-disable-line
+      closeOnClick,
       title,
       ...rest
     } = this.props;

eslint.config.mjs

@@ -0,0 +1,87 @@
+import { merge } from 'min-dash';
+
+import globals from 'globals';
+
+import bpmnIoPlugin from 'eslint-plugin-bpmn-io';
+import camundaLicensedPlugin from 'eslint-plugin-camunda-licensed';
+
+export default [
+  ...camundaLicensedPlugin.configs.mit.map((config) => {
+    return {
+      ...config,
+      files: [
+        'app/lib/**/*.js',
+        'client/src/**/*.js'
+      ]
+    }
+  }),
+  ...bpmnIoPlugin.configs.node.map((config) => {
+    return merge({
+      ...config,
+      files: [
+        'app/lib/**/*.js',
+        'resources/**/*.js',
+        'tasks/**/*.js'
+      ]
+    }, {
+      languageOptions: {
+        globals: {
+          ...globals.chai,
+          ...globals.mocha
+        }
+      }
+    })
+  }),
+  ...bpmnIoPlugin.configs.mocha.map((config) => {
+    return {
+      ...config,
+      files: [
+        '**/__tests__/**/*.js',
+        'test/**/*.js'
+      ]
+    };
+  }),
+  ...bpmnIoPlugin.configs.browser.map((config) => {
+    return merge({
+      ...config,
+      files: [
+        'client/src/**/*.js',
+        'resources/plugins/**/*.js'
+      ]
+    }, {
+      languageOptions: {
+        globals: {
+          ...globals.chai,
+          ...globals.mocha,
+          ...globals.node
+        }
+      }
+    });
+  }),
+  ...bpmnIoPlugin.configs.jsx.map((config) => {
+    return merge({
+      ...config,
+      files: [
+        'client/src/**/*.js',
+        'resources/plugins/**/*.js'
+      ]
+    }, {
+      rules: {
+        'react/jsx-uses-react': 'error',
+        'react/react-in-jsx-scope': 'error'
+      }
+    });
+  }),
+  {
+    ignores: [
+      '**/dist',
+      '**/node_modules',
+      'app/public',
+      'app/preload',
+      'client/build',
+      'coverage',
+      'docs',
+      'tmp'
+    ]
+  }
+];