Extend interface with masking operations.

[edanor]

Originally reported by: edanor (Bitbucket: edanor, GitHub: edanor)

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As for other interfaces, masks should also implement MFI functions with masking operand. An example where it causes problems comes from VecGeom:

VECGEOM_FORCE_INLINE
void MaskedAssign(UmesimdBool_v const &cond, UmesimdBool_v const &thenval, UmesimdBool_v *const output)
{
//output->assign(cond, thenval);
UmesimdBool_v out_v;
out_v.assign(*output);
UmesimdBool_v t0 = cond.land(thenval);
UmesimdBool_v t1 = (!cond).land(out_v);
UmesimdBool_v t2 = t0 || t1;
output->assign(t2);
}

here the overloaded 'MaskedAssign' operation tries to perform blending between two masks.

If usage model comes from the users it should be provided automatically.

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• Bitbucket: https://bitbucket.org/edanor/umesimd/issue/35