Bump ffigen from 15.0.0 to 16.0.0 in /experimental/pedometer

Bumps [ffigen](https://github.com/dart-lang/native/tree/main/pkgs) from 15.0.0 to 16.0.0.
- [Release notes](https://github.com/dart-lang/native/releases)
- [Commits](https://github.com/dart-lang/native/commits/HEAD/pkgs)

---
updated-dependencies:
- dependency-name: ffigen
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

experimental/pedometer/pubspec.yaml

@@ -14,7 +14,7 @@ dependencies:
   ffi: ^2.1.2
 
 dev_dependencies:
-  ffigen: ^15.0.0
+  ffigen: ^16.0.0
   jnigen: ^0.12.1
   flutter_test:
     sdk: flutter