Spring Check for valid IPv6 host in UriComponentsBuilder.fromUriString

Overview

PR #358 introduced a "scheme but no host" check in the fromHttpUrl method in UriComponentsBuilder, but a similar check was not added to fromUriString.

Deliverables

• [x] Introduce a "scheme but no host" check in UriComponentsBuilder.fromUriString to align with the functionality in fromHttpUrl.