These APIs started out as private APIs in qnumeric_p.h, but have since
been made pseudo-public in qnumeric.h. The qnumeric_p.h versions just
forward to the qnumeric.h ones, so just use the latter.
This is in preparation of removing the {add,sub,mul}_overflow
versions, which, despite being defined in the unnamed namespace, don't
sport the q prefix, so potentially clash with global symbols.
The change is a simple textual search and replace, manually excluding
qnumeric_p.h.
Picking to 6.5 to avoid cherry-pick conflicts going forward.
Pick-to: 6.6 6.5
Change-Id: Ic0f7c92f7c47923317109e8a9dc06fa66bdff2c2
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>