[CIR] Upstream TernaryOp (#137184)
This patch adds TernaryOp to CIR plus a pass that flattens the operator
in FlattenCFG.
This is the first PR out of (probably) 3 wrt. TernaryOp. I split the
patches up to make reviewing them easier. As such, this PR is only about
adding the CIR operation. The next PR will be about the CodeGen bits
from the C++ conditional operator and the final one will add the
cir-simplify transform for TernaryOp and SelectOp.
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Co-authored-by: Morris Hafner <mhafner@nvidia.com>
Co-authored-by: Andy Kaylor <akaylor@nvidia.com>
