[Cranelift] add simplification rules

[myunbin]

This PR adds several simplification rules:

bitops.isle

• (~x & y) ^ x --> x | y
• (x | y) & ~(x ^ y) --> x & y
• x | ~(x ^ y) --> x | ~y
• x | ((~x) ^ y) --> x | ~y
• x & ~(x ^ y) --> x & y
• x & ((~x) ^ y) --> x & y
• (x | y) | (x ^ y) --> (x | y)
• (x ^ y) & (x ^ (y ^ z)) --> (x ^ y) & ~z
• (~x & y) ^ z --> (x & y) ^ (z ^ y)
• ~x - ~y --> y - x
• (~x & y) | ~(x | y) --> ~x
• (~x | y) & ~(x & y) --> ~x
• (x & y) | ~(x | y) --> ~(x ^ y)
• (~x | y) ^ (x ^ y) --> x | ~y

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[fitzgen]

Thanks!