[flutter_tools] migrate some integration tests to null safety by @jonahwilliams in https://github.com/flutter/flutter/pull/103560

Enforce minimum plugin version iOS 11 by @jmagman in https://github.com/flutter/flutter/pull/103545

[flutter_tools] remove assertion for deprecation .packages by @jonahwilliams in https://github.com/flutter/flutter/pull/103729

[flutter_tools] ensure linux doctor validator finishes when pkg-config is not installed by @christopherfujino in https://github.com/flutter/flutter/pull/103755

Fix deprecation doc comment by @cbracken in https://github.com/flutter/flutter/pull/103776

[tool] Fix BuildInfo.packagesPath doc comment by @cbracken in https://github.com/flutter/flutter/pull/103785