CHANGELOG: consolidate `dart:core` for 1.19 and fix link
CHANGELOG: consolidate `dart:core` for 1.19 and fix link

Change-Id: Ieacc901aea121418782e938133670eef2d8732fd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/265901
Reviewed-by: Devon Carew <e996497f4f2225f0ee7a9f4d1696ee710b488b66@google.com>
Commit-Queue: Devon Carew <e996497f4f2225f0ee7a9f4d1696ee710b488b66@google.com>
Auto-Submit: Kevin Moore <1d6e7d10d051cf619c5282da3c28fd8d3e0a65a4@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk