cc_test mixed builds: suffix bazel label with __tf_internal.

To support `b test //path/to:my_test` command line, the actual
executable in the cc_test macro now has the __tf_internal suffix in its
name, so that the top level test suite target can be named without any suffixes.

See other CLs in this topic for more info.

Test: presubmits
Fixes: 292159775
Change-Id: I2d0bfc4276717ae881f6f3eb6aefa88bb47f25da