[X86] Refactor MatchVectorAllZeroTest -> MatchVectorAllEqualTest

Refactor MatchVectorAllZeroTest to work with allof/anyof/noneof comparisons with -1 as well as 0, and use it handle icmp(bitcast(icmp_eq(X,Y)),-1) reduction patterns.

We're still missing test coverage for other other reduction types, so have kept these limited to icmp X,0 for now.