[X86] Don't assume an AND/ANDNP element is undef/undemanded just because one element is undef

For mask ops like these, the other operand's corresponding element might be zero (result = zero) - so we must demand all the bits and that element.

This appears to be what D128570 was trying to fix - both sides of the funnel shift mask of the vXi64 (legalized to v2Xi32) were incorrectly simplifying the upper 32-bit halves to undef, resulting in bad folds later on.

I intend to address the test case regressions, but this close to the release branch I'd prefer to get a fix in first.