[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: https://github.com/flutter/flutter/issues/178270
Manual fixes:
- Updates camera_android_camerax and webview_flutter_android for https://github.com/flutter/packages/pull/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.
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[interactive_media_ads] Pin iOS dependency maximum (#10349)
GoogleInteractiveMediaAds [released 3.28.10](https://github.com/googleads/swift-package-manager-google-interactive-media-ads-ios/commit/7f38970c871ce30e214705058a8a1fbd397dff030) which dropped iOS 13 and 14, breaking our tree. This sets a max version on the dependency to avoid picking up a version that is not compatible with our wrapper's iOS version support.
Longer term we can explore expanding the range, but this is non-trivial for Swift Package Manager, so this is the simplest way to fix the tree and clients in the short term.
## Pre-Review Checklist
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