A very basic implementation of the proposed std::array_view, similar to
clang's llvm::ArrayRef.

Mostly cribbed from the string_view implementation :-)

Use it for the SfxDispatcher::setSlotFilter function

Change-Id: Ife7e4971741b41827e145787899872c9b2bea82b
Reviewed-on: https://gerrit.libreoffice.org/38817Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>