fix(eslint-plugin): [consistent-indexed-object-style] convert readonly index signature to readonly record

packages/eslint-plugin/docs/rules/consistent-indexed-object-style.md

@@ -46,6 +46,14 @@ Examples of **correct** code with `record` option.
 
 ```ts
 type Foo = Record<string, unknown>;
+
+interface Foo {
+  readonly [key: string]: unknown;
+}
+
+type Foo = {
+  readonly [key: string]: unknown;
+};
 ```
 
 Examples of **incorrect** code with `index-signature` option.

packages/eslint-plugin/src/rules/consistent-indexed-object-style.ts

@@ -76,6 +76,10 @@ export default createRule<Options, MessageIds>({
         return;
       }
 
+      if (member.readonly) {
+        return;
+      }
+
       const [parameter] = member.parameters;
 
       if (!parameter) {

packages/eslint-plugin/tests/rules/consistent-indexed-object-style.test.ts

@@ -51,6 +51,18 @@ type Foo = {
 };
     `,
 
+    // Readonly
+    `
+interface Foo {
+  readonly [key: string]: any;
+}
+    `,
+    `
+type Foo = {
+  readonly [key: string]: any;
+};
+    `,
+
     // Generic
     `
 type Foo = Generic<{