Add vmodule support to TF OSS logging.

Setting the environment variable TF_CPP_VMODULE=foo=7,bar=7 will cause the
"foo" and "bar" translation units (foo.{h.cc},bar.{h.cc}) to have a VLOG level
of 7, meaning VLOG(0) to VLOG(7) in those translation units will be logged to
stderr (as LOG(ERROR) does).

PiperOrigin-RevId: 222927031