The files in this directory specifies pinned versions of various dependencies of the flutter SDK.
The bin/internal/engine.version file controls where to find compiled artifacts of the engine. These artifacts are compiled in the Merge Queue for every commit in the flutter repository.
The bin/internal/flutter_packages.version file specifies the version of the flutter/packages repository to be used for testing. The flutter/packages repository isn't an upstream dependency of flutter/flutter; it is only used as part of the test suite for verification, and the pinned version here makes sure that tests are deterministic at each flutter/flutter commit.