Revert "Roll engine f6af1f20ba92..b59c86493159 (3 commits)" (#22559)

* Revert "unnecessary this in field initializers (#22522)"

This reverts commit 5de96bb7341c521f7a6a3dec8cf24628aa1aa3e7.

* Revert "Use unsafePackageSerialization when running tests (#22407)"

This reverts commit 4bd6ad73954e42a98003a6e23502df0487ff5dfd.

* Revert "Roll engine f6af1f20ba92..b59c86493159 (3 commits) (#22538)"

This reverts commit 85a4591aa329a4c304063ea3d54d2bd742b29836.

bin/internal/engine.version

diff --git a/bin/internal/engine.version b/bin/internal/engine.version
index ab59984..22d2ab5 100644
--- a/bin/internal/engine.version
+++ b/bin/internal/engine.version
@@ -1 +1 @@
-b59c86493159febde740cf5359b8ce867213c19a
+f6af1f20ba92a819401d66ae4b2179b0775b0e12