...and revert the relevant part of 2f5f45921b
"support O(U)String::number() for fast string concatenation", as discussed in
the comments of that Gerrit change, now that
89bb0b0dcd "Deduplicate O(U)StringNumber
definitions; add toAsciiUpperCase" paved the way.
For consistency, also add conversion from rtl::OUStringNumber to
std::u16string_view, even if that remains unused as of now.
Change-Id: Ieb64bff0b59c22f3dec05c99fca5676b27a46e9a
Reviewed-on: https://gerrit.libreoffice.org/79750
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
