chore: convert ESLint files from .js/.mjs to .ts (#109310)

Directly changes files from `.mjs` to ~`.mts`. I would have preferred
the cleaner `.ts` but that will require adding `"type": "module"` to
`package.json`, which is more work (which would be a great followup!).~
`.ts`, building on #109319's switching the package to be ESM by default.
Imports are now TypeScript-style extension-less ones.

Now that the plugin's files are typed, this applies a few types
cleanups:

* Uses [typescript-eslint's
`RuleCreator`](https://typescript-eslint.io/developers/custom-rules#rulecreator)
to create rules, which gives nicer typings than the built-in ESLint
`Rule`
* Updates node types from [`estree`](https://github.com/estree/estree)
(only vanilla JS types) to
[`@typescript-eslint/estree`](https://typescript-eslint.io/packages/typescript-estree)
(full TS node types)
* Converts JSDoc types to full TypeScript syntax

This PR should have no changes to the lint rules' behavior. The only
runtime code changes are for deleting unused parameters.

Author: JoshuaKGoldberg

.github/CODEOWNERS

@@ -118,7 +118,7 @@ vercel.json                                              @getsentry/owners-js-bu
 /.github/file-filters.yml                                @getsentry/owners-js-build
 babel.config.*                                           @getsentry/owners-js-build
 build-utils/                                             @getsentry/owners-js-build
-eslint.config.js                                         @getsentry/owners-js-build
+eslint.config.ts                                         @getsentry/owners-js-build
 jest-balance.json                                        @getsentry/owners-js-build
 jest.config.ts                                           @getsentry/owners-js-build
 tsconfig.*                                               @getsentry/owners-js-build

eslint.config.js eslint.config.tseslint.config.js renamed to eslint.config.ts

@@ -49,9 +49,9 @@ import invariant from 'invariant';
 import typescript from 'typescript-eslint';
 
 // eslint-disable-next-line boundaries/element-types
-import * as sentryScrapsPlugin from './static/eslint/eslintPluginScraps/index.js';
+import * as sentryScrapsPlugin from './static/eslint/eslintPluginScraps/index';
 // eslint-disable-next-line boundaries/element-types
-import * as sentryPlugin from './static/eslint/eslintPluginSentry/index.js';
+import * as sentryPlugin from './static/eslint/eslintPluginSentry/index';
 
 invariant(react.configs.flat, 'For typescript');
 invariant(react.configs.flat.recommended, 'For typescript');
@@ -431,7 +431,7 @@ export default typescript.config([
       'import/no-duplicates': 'error',
       'import/no-extraneous-dependencies': [
         'error',
-        {includeTypes: true, devDependencies: ['!eslint.config.js']},
+        {includeTypes: true, devDependencies: ['!eslint.config.ts']},
       ],
       'import/no-named-default': 'error',
       'import/no-nodejs-modules': 'error',

knip.config.ts

@@ -44,7 +44,7 @@ const config: KnipConfig = {
     ...productionEntryPoints.map(entry => `${entry}!`),
     ...testingEntryPoints,
     ...storyBookEntryPoints,
-    'static/eslint/**/index.js',
+    'static/eslint/**/index.ts',
     // figma code connect files - consumed by Figma CLI
     'static/**/*.figma.{tsx,jsx}',
   ],
@@ -60,7 +60,7 @@ const config: KnipConfig = {
     '!static/app/**/__stories__/*.{js,ts,tsx}!',
     '!static/app/stories/**/*.{js,ts,tsx}!',
     // ignore eslint plugins in production
-    '!static/eslint/**/*.js!',
+    '!static/eslint/**/*.ts!',
   ],
   compilers: {
     mdx: async text => String(await compile(text)),

package.json

@@ -204,6 +204,8 @@
     "@types/gettext-parser": "8.0.0",
     "@types/node": "^22.9.1",
     "@typescript/native-preview": "7.0.0-dev.20260112.1",
+    "@typescript-eslint/utils": "8.56.1",
+    "@typescript-eslint/rule-tester": "8.56.1",
     "babel-jest": "30.0.4",
     "eslint": "9.34.0",
     "eslint-config-prettier": "10.1.8",