Roll Flutter Engine from 990f1ceac5d5 to 40b868efcc46 (2 revisions) (#…

…149462)

flutter/engine@990f1ce...40b868e

2024-05-31 jonahwilliams@google.com [Impeller] make strokes < 0.5 physical pixels visually thinner. (flutter/engine#53154)
2024-05-31 jonahwilliams@google.com [Impeller] Replace Impeller opacity peephole delegate with DL variant. (flutter/engine#52707)

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/flutter-engine-flutter-autoroll
Please CC jacksongardner@google.com,rmistry@google.com,zra@google.com on the revert to ensure that a human
is aware of the problem.

To file a bug in Flutter: https://github.com/flutter/flutter/issues/new/choose

To report a problem with the AutoRoller itself, please file a bug:
https://issues.skia.org/issues/new?component=1389291&template=1850622

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

bin/internal/engine.version

@@ -1 +1 @@
-990f1ceac5d57225459df25e403afa437cad120a
+40b868efcc46bdcfa84a03632bb5f61a5d6b04f4