Release dwds 20.0.2 and webdev v3.0.8, then retract 3.0.7

[parlough]

Release dwds 20.0.2 and webdev v3.0.8, then consider retracting 3.0.7.

This is to fix dart-lang/sdk#53459 after #2207 lands.

There are other potential solutions. Just opening this issue to track it.

[parlough]

Closing in favor of plan at dart-lang/sdk#53459 (comment). Thanks!