Roll engine to 6a93ef1c707fb1fdea697a1c35bf68fc4e2986e3 (#16946)

flutter/engine@6a93ef1 Call SkGraphics::Init earlier on Fuchsia.
flutter/engine@f1234eb Add disabled failing test for floating point errors on matrix decomposition.
flutter/engine@ac68263 Hold a global reference to the AssetManager Java object backing the APKAssetProvider
flutter/engine@0e95bb2 Roll src/third_party/skia/ 2d2c1e32c..058f2e6ed (35 commits; 1 trivial rolls)
flutter/engine@3e20562 Roll src/third_party/skia/ 5209d7fce..2d2c1e32c (42 commits; 1 trivial rolls)
flutter/engine@a20fd83 [fuchsia] Remove dead package file generation from core snapshots.
flutter/engine@79b9ffb Fixup Fuchsia content handler post shell refactor.

bin/internal/engine.version

-ec611470b571c35156723a163fdcacd1f58b1809
+6a93ef1c707fb1fdea697a1c35bf68fc4e2986e3