dds package should migrate to null safety #45756
Description
dds 1.7.6 is not null safe:
Line 5 in 96cf91b
This is preventing the flutter_tool from migrating its size analyzer library to null safety.
https://github.com/flutter/flutter/blob/6b3093b6afd6a47e57c07f7e3f701d5e97073fc8/packages/flutter_tools/lib/src/base/dds.dart#L9
\cc @bkonyi