Split test compilation and code generation into two targets.
Split test compilation and code generation into two targets.

Since we need specific deps for code generation in j2cl_test users can get away without specifying these dependencies themselves. This change splits up srcs complilation (all deps most be specified by the user) and our code generation into two separate targets.

PiperOrigin-RevId: 140087363

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