These libraries will be shared between the dart2js and DDC runtimes.
Also renames the `shared` directory to `synced` to avoid confusion.
Synced directories are copied to be in sync with the compilers and
runtimes.
Change-Id: Ic36076938741d7102792f09413666de0033da3a4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/238300
Reviewed-by: Mayank Patke <fishythefish@google.com>
Reviewed-by: Ivan Inozemtsev <iinozemtsev@google.com>
Reviewed-by: Stephen Adams <sra@google.com>
Commit-Queue: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Nate Bosch <nbosch@google.com>