Roll engine 905c571db50d..72986c39ea36 (2 commits) (#30861)

https://github.com/flutter/engine/compare/905c571db50d...72986c39ea36

git log 905c571db50d5eb3b10eaa4d3c43c99321032223..72986c39ea3669ef26d4d7d7cd0c44f513fcd117 --no-merges --oneline
72986c39e Move constant definitions out embedder.h (flutter/engine#8498)
e356dbca2 Merge flutter/synchronization contents into fml. (flutter/engine#8525)

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bin/internal/engine.version

-905c571db50d5eb3b10eaa4d3c43c99321032223
+72986c39ea3669ef26d4d7d7cd0c44f513fcd117