common/strtol: expose strict_si_cast(std::string_view, ..)

common/strtol: expose strict_si_cast(std::string_view, ..)

this variant is better than strict_si_cast(const char*), because:

* we can just pass std::string to it, as std::string_view can be
  constructed from a std::string implicitly
* strict_si_cast(std::string_view, ..) is the underlying
  implementation of strict_si_cast(const char*,..), so less
  indirection helps with the readability.

Signed-off-by: Kefu Chai <kchai@redhat.com>