6bdd38ae84
This is a reland of 1702b986c8
Original change's description:
> Move the JavaScript constant system into constants/constant_system.dart
> in preparation to merge it with the base constant system and flatten the
> constant system hierarchy.
>
> Change-Id: I6ef27b210515140d4516336fea015f74c8a0cd6a
> Reviewed-on: https://dart-review.googlesource.com/c/93840
> Reviewed-by: Sigmund Cherem <sigmund@google.com>
> Reviewed-by: Johnni Winther <johnniwinther@google.com>
Change-Id: I20ef9755886a6b54135aa7169c9d7de08e8cbe93
Reviewed-on: https://dart-review.googlesource.com/c/94105
Reviewed-by: Sigmund Cherem <sigmund@google.com>