spirv-opt: Adding nested reassociation rules (KhronosGroup#6453)

**ReassociateNestedGenericInt**
Reassociate integer instructions where both operands share the same
opcode and both source instructions contain a constant.
e.g:
```
  (a * C0) * (C1 * b) = (C0 * C1) * (a * b)
  (a ^ C0) ^ (b ^ C1) = (C0 ^ C1) ^ (a ^ b)
  (C0 | a) | (b | C1) = (C0 | C1) | (a | b)
  (a & C0) & (b & C1) = (C0 & C1) & (a & b)
```

**ReassociateNestedMulDivFloat**
Reassociate floating point mul/div instructions, which have mul/div
inputs, both of which contain a constant.
e.g:
```
  (a * C0) / (C1 / b) =  (C0 / C1) * (a * b)
  (C0 / a) * (b / C1) =  (C0 / C1) * (b / a)
  (a / C0) / (b * C1) =  (1 / (C0 * C1)) * (a / b)
```

**ReassociateNestedAddSub**
Reassociate add/sub instructions, which have add/sub inputs, both of
which contain a constant.
e.g:
```
  (a + C0) - (C1 - b) =  (C0 - C1) + (a + b)
  (C0 - a) + (b - C1) =  (C0 - C1) + (b - a)
  (a - C0) - (b + C1) = (-C0 - C1) + (a - b)
```

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Co-authored-by: Steven Perron <[email protected]>

Author: alister-chowdhury