None of the weld::Box methods are used, so having a pointer
to the weld::Container subclass is sufficient in the
"Find and Replace" dialog implementation.
Change-Id: I1219dd657ab8fb6067c90aabdc27b2b84c0a1443
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/177577
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>
