Cranelift: add mid-end opt rules

[myunbin]

Add mid-end optimization rules:

• sextend(x) OP sextend(y) --> x OP y where OP = {==, <s}
• rotr(x, k) == rotr(y, k) --> x == y
• select(c, x, y) OP select(c, y, x) --> x OP y, where OP = {&, |, ^}
• select(x == y, 0, x ^ y) --> x ^ y
• select(x != y, x ^ y, 0) --> x ^ y
• select(k == 0, x, x OP k) --> x OP k, where OP= {ishl, ushr, sshr, rotl, rotr} and its dual(k != 0).

Thanks!

[github-actions]

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cc @avanhatt, @cfallin, @fitzgen, @mmcloughlin

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