[MCA] Use Bare Reference for InstrPostProcess (#160229)
This patch makes it so that InstrPostProcess::postProcessInstruction
takes in a reference to a mca::Instruction rather than a reference to a
std::unique_ptr. Without this, InstrPostProcess cannot be used with MCA
instruction recycling because it needs to be called on both newly
created instructions and instructions that have been recycled. We only
have access to a raw pointer for instructions that have been recycled
rather than a reference to the std::unique_ptr that owns them.
This patch adds a call in the existing instruction recycling unit test
to ensure the API remains compatible with this use case.
