[TTI][X86] Recognise PMULUDQ costs for vXi64 multiplies

Addresses part of Issue #62969 - if the upper 32-bits of the vXi64 elements are known to be zero, then a multiply simplifies to a single (fast) PMULUDQ instruction

We still have the problem that minRequiredElementSize can't determine that the upper bits are zero for the test case from Issue #62969 - I'll take a look at that next.