Revert "Remove dependency on package:charcode (dart-lang/string_scanner#29)" (dart-lang/string_scanner#33)

This reverts commit d769b0e6c94945d29b83175ed06f9eaec1571cbb.

Since this has not been published or rolled through to the SDK or
Flutter we will hold it back to reduce risk.
7 files changed
tree: a73f8b863cd800a3c6fe1328cdeb719673447274
  1. pkgs/