Concerns about the usage of `--dart-define` in gradle scripts

[vanyasem]

In #1111, it was decided to use dart-define to determine dependency, and it's used in build.gradle: https://github.com/dart-lang/http/pull/1111/files#diff-7eec577c9e03d491b0cd36f6123f52011707d1c3e96bce8ce875629a057f4046

As discussed in flutter/flutter#136865 (comment), the fact that --dart-define happens to provide it's value to gradle is an undocumented implementation detail, and should not be relied upon

The issue for the implementation of a proper way to pass params to native build tools is located here: flutter/flutter#139289

Some additional context can be found here: flutter/flutter#138793