core: add custom function to check emergency URN

[anmartan]

Pre-Submission Checklist

• Commit message has the format required by CONTRIBUTING guide
• Commits are split per component (core, individual modules, libs, utils, ...)
• Each component has a single commit (if not, squash them into one commit)
• No commits to README files for modules (changes must be done to docbook files
  in doc/ subfolder, the README file is autogenerated)

Type Of Change

• Small bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds new functionality)
• Breaking change (fix or feature that would change existing functionality)

Checklist:

• PR should be backported to stable branches
• Tested changes locally
• Related to issue #XXXX (replace XXXX with an open issue number)

Description

Improved URN parsing according to RFC8141 that allows an arbitrary number of colons to be present in the URN value. Entire URN NID and NSS parts (except for urn: scheme) are stored in the uri.host struct field. rq-components are not supported.

Example of the parse error when parsing "urn:emergency:service:sos"

parse_uri(): bad char ':' in state 3 parsed: urn:emergency:service (21) / urn:emergency:service:sos (25)

URN values that have been tested to work:

• urn:emergency:service:sos
• urn:emergency:responder.fire
• urn:emergency:media-feature

[IvanRibakov]

Looks good to proceed!