Add support for folding constant unary non-compute ops in RTVar optimization
Add support for folding constant unary non-compute ops in RTVar optimization

So far we can only optimize away RTVars that refer to a `constant` or `iota`
HLO op. This change is extending that to unary ops without compute (given
the operand is also constant).

That includes:
- Bitcast
- Broadcast
- Reshape
- Reverse
- Slice
- Transpose
