[various] Update all packages to Pigeon 26 (#10450)

Pigeon versions <26.0.4 aren't compatible with `analyzer` 8.x, which is causing conflicts for flutter/flutter, so this updates the entire repo to 26.

Related: flutter/flutter#178270

Manual fixes:
- Updates `camera_android_camerax` and `webview_flutter_android` for #9515
- Adds the `pigeonVar_*` overrides to the `url_launcher_windows` tests
- Removes equality extensions to Pigeon data classes in `in_app_purchase_storekit`, as they are now generated by Pigeon, causing redeclaration errors.

## Pre-Review Checklist

[^1]: Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling.

Author: stuartmorgan-g

packages/camera/camera_android/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.10.10+13
+
+* Updates to Pigeon 26.
+
 ## 0.10.10+12
 
 * Removed mockito-inline and updated to mockito-core 5.17.0.

packages/camera/camera_android/android/src/main/java/io/flutter/plugins/camera/Messages.java

@@ -1,7 +1,7 @@
 // Copyright 2013 The Flutter Authors
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-// Autogenerated from Pigeon (v22.4.1), do not edit directly.
+// Autogenerated from Pigeon (v26.1.0), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 package io.flutter.plugins.camera;