v0.21.0

What's Changed

• fix(shorebird_cli): use aot-tools.dill for linking if available by @bryanoltman in #1596
• chore: update to Flutter 3.16.5 by @bryanoltman in #1607
• chore(shorebird_cli): draft 0.21.0 release by @bryanoltman in #1608

Full Changelog: v0.20.0...v0.21.0