Automated g4 rollback of changelist 237521264.
Automated g4 rollback of changelist 237521264.

*** Reason for rollback ***

Need blueprint files update

*** Original change description ***

Move jsinterop-base in its own repository.

I tried to minimize files changes. Any other cleanup (copybara/kokoro/BUILD...) will be done in follow-up CLs.

***

PiperOrigin-RevId: 237528510

google/j2cl,google/j2cl,google/j2cl,google/j2cl,google/j2cl