Update SplitCommandLine test helper names
Update SplitCommandLine test helper names

This must have been called SplitStartupOptions at some point? Either way, the
tests are for SplitCommandLine, so that's what the methods should be called to
make them easy to find.

PiperOrigin-RevId: 450027186

cushon/bazel,bazelbuild/bazel,bazelbuild/bazel,katre/bazel,cushon/bazel,cushon/bazel,katre/bazel,bazelbuild/bazel,cushon/bazel,katre/bazel,cushon/bazel,katre/bazel,bazelbuild/bazel,katre/bazel,cushon/bazel,bazelbuild/bazel,bazelbuild/bazel,katre/bazel