Roll engine 288a855bfd8e..9d7cd70ce534 (3 commits) (#32837)

https://github.com/flutter/engine/compare/288a855bfd8e...9d7cd70ce534

git log 288a855bfd8e0f32024b1457319def24b47670e7..9d7cd70ce5346d1c8bf1d1a3595cdc9f314c0825 --no-merges --oneline
9d7cd70ce add observatoryUrl property to FlutterEngine (flutter/engine#8987)
34a524837 Add matrix4 param to Linear gradients (flutter/engine#8985)
aa63f090f libtxt: add a BoxHeightStyle option based on the height of the strut (flutter/engine#8927)

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bin/internal/engine.version

-288a855bfd8e0f32024b1457319def24b47670e7
+9d7cd70ce5346d1c8bf1d1a3595cdc9f314c0825