flutter_test dependency in dynamic_color

[vauvenal5]

Existing issue?

• I checked the existing issues

What happened?

I was wondering why DynamicColorTestingUtils is part of lib and therefor forcing flutter_test to be a dependency.

I also looked into this PR #638 which was reverted down the line and was wondering about the actual issues it caused?

If DynamicColorTestingUtils is to be provided to users of the package, would it make sense to move it into its own package not forcing flutter_test as a dev dependency?

[vauvenal5]

I guess what I am asking is, may I simply move DynamicColorTestingUtils into the test package if its not used anywhere else anyway?

[vauvenal5]

I created a draft PR to have something to look at. ☝️

Happy to hear some feedback on this matter. :)