Roll engine dd6be2fd8371..af64f725f6c7 (3 commits) (#29944)

https://github.com/flutter/engine/compare/dd6be2fd8371...af64f725f6c7

git log dd6be2fd83710de8392fb554927a5d495684a13e..af64f725f6c74f5d1287a8be8511691119354088 --no-merges --oneline
af64f725f Fixing links between higher and lower classes. (flutter/engine#8295)
22ee8ee08 Migrate existing embedder unit tests to use the fixture. (flutter/engine#8296)
345ae7d37 Delegate a11y events and action to/from embedded Android platform views. (flutter/engine#8250)

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bin/internal/engine.version

-dd6be2fd83710de8392fb554927a5d495684a13e
+af64f725f6c74f5d1287a8be8511691119354088