* Roll engine to c88ba37c794f57982374bb53a694301198cad593.

Changes since last roll:
  - move generated entry points JSON out of flutter_patched_sdk
  - List missing core lib bigint_patch.dart source for new Bigint implementation (#4735)
  - Skip over .emf-files. (#4739)
  - Roll dart to ee15c8eb689791f6777eb3f6b0a1e9c58ff0671b.

* defaultValue -> orElse