Migrate to ESLint 9 (#10762)

* update ESLint related packages

* migrate to flat config format

* Fix prefer-const error

Fixes
'overrideLogoSize' is never reassigned. Use 'const' instead

* remove irrelevant eslint-disable comment

These comments came from a swizzled upstream
component but never did anything in our codebase.

ESLint 9 does not allow disable comments
for rules that are not registered.

* remove irrelevant eslint-disable comments

These were here because in the past we were applying
mocha lint rules to files which contained no tests

ESLint 9 now flags eslint-disable comments
that aren't doing anythings

* remove irrelevant eslint-disable comment

ESLint 9 now flags eslint-disable comments
that aren't doing anything

* there are no .tsx files in our code any more

* include .mjs files in linting and formatting

* update sort-class-members rule for openApi property

and update the handful of files violating it

core/base-service/coalesce-badge.js

@@ -47,13 +47,13 @@ export default function coalesceBadge(
     label: overrideLabel,
     logo: overrideLogo,
     logoColor: overrideLogoColor,
+    logoSize: overrideLogoSize,
     link: overrideLink,
     colorB: legacyOverrideColor,
     colorA: legacyOverrideLabelColor,
   } = overrides
   let {
     logoWidth: overrideLogoWidth,
-    logoSize: overrideLogoSize,
     color: overrideColor,
     labelColor: overrideLabelColor,
   } = overrides

core/base-service/legacy-request-handler.js

@@ -115,7 +115,6 @@ function handleRequest(cacheHeaderConfig, handlerOptions) {
     const result = handlerOptions.handler(
       filteredQueryParams,
       match,
-      // eslint-disable-next-line mocha/prefer-arrow-callback
       function sendBadge(format, badgeData) {
         if (serverUnresponsive) {
           return
@@ -128,7 +127,6 @@ function handleRequest(cacheHeaderConfig, handlerOptions) {
         makeSend(format, ask.res, end)(svg)
       },
     )
-    // eslint-disable-next-line promise/prefer-await-to-then
     if (result && result.catch) {
       // eslint-disable-next-line promise/prefer-await-to-then
       result.catch(err => {

core/service-test-runner/service-tester.js

@@ -83,7 +83,7 @@ class ServiceTester {
       .before(() => {
         this.beforeEach()
       })
-      // eslint-disable-next-line mocha/prefer-arrow-callback, promise/prefer-await-to-then
+      // eslint-disable-next-line promise/prefer-await-to-then
       .finally(function () {
         // `this` is the IcedFrisby instance.
         let responseBody