[pigeon] Adds support for analyzer 10

[tarrinneal]

minimal required changes

fixes flutter/flutter#183568

[flutter-dashboard]

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[gemini-code-assist]

Code Review

This pull request updates the pigeon package version to 26.2.4 and extends the supported range for the analyzer dependency to include versions up to <11.0.0. The CHANGELOG.md and generator_tools.dart files are updated to reflect this version bump. The reviewer noted that the pull request description should be updated to include the Pre-Review Checklist as required by the repository's style guide.

[stuartmorgan-g]

LGTM with nit