Any URLs using non-ASCII IDNA syntax need to be resolved to ASCII-only, as PDF
URI Action's URI needs to be "encoded in 7-bit ASCII."

Introduce URIHelper::resolveIdnaHost (svl/urihelper.hxx), which internally uses
icu::IDNA, which requires to bump the minimal --with-system-icu requirement from
4.2 to 4.6, which means ICU_RECLASSIFIED_CLOSE_PARENTHESIS is always true now.

Change-Id: I0e20d9a20ed2b869fba0cc7c969721411db590b3
Reviewed-on: https://gerrit.libreoffice.org/19669Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Stephan Bergmann <sbergman@redhat.com>