Migrate dwds to null safety

[jmagman]

dwds 11.0.2 is not null safe:

webdev/dwds/lib/dwds.dart

Line 5 in b851f74

// @dart = 2.9

This is preventing the flutter_tool from migrating to null safety.
https://github.com/flutter/flutter/blob/4a33813b3500308bb579a1dad5560971baec899f/packages/flutter_tools/lib/src/isolated/resident_web_runner.dart#L9

Note dds just published a null safe 2.0 dart-lang/sdk#45756.

[jmagman]

\cc @jonahwilliams

[grouma]

What's the priority here?

[jonahwilliams]

This is low priority but nice to have

[devoncarew]

Is this issue complete (package:dwds is now null safe?)?

[devoncarew]

ping @elliette - do you know the status here?

[elliette]

All files have been migrated and DWDS is now null-safe, but the null-safe version has not yet been released (planning to do that this week)

[devoncarew]

Thanks! Can you update this (and #1640) when that happens?

[elliette]

Just published null-safe DWDS (v.16.0.0), therefore closing as completed.