Improve URI option decomposition to better match CoAP RFC 7252

[frantp]

This PR updates the URI decomposition logic to better conform to the CoAP specification (section 6.4), addressing the following points:

• Uri-Host (Point 5)

  If the component of |url| does not represent the request's destination IP address as an IP-literal or IPv4address, include a Uri-Host Option [...]

  The implementation now omits the Uri-Host option when the <host> component is an IP address.

• Uri-Query (Point 9)

  [...] for each argument in the component, include a Uri-Query Option and let that option's value be the argument (not including the question mark and the delimiting ampersand characters) [...]

  Query arguments are now correctly split and included as separate Uri-Query options. The API for RequestBuilder is modified to support this change.

[Covertness]

LGTM