Initial copy elision pass (#8042)

Fixes #7574

Changes:
* Add an initial (fairly simple) optimization pass which is able to
eliminate redundant copies.
* Our current existing optimizer passes remove redundant load/store very
robustly, this pass will focus on other cases of copy elimination
* Primary approach is to make all functions which are `in T` and `T` is
trivial to copy into a `__constref T`. We then (depending on scenario)
manually insert a variable+load if a pass-by-reference is not possible;
otherwise we pass by `constref`.
* Added optimizations to eliminate redundant code which causes
`constref` to fail to compile

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Co-authored-by: Harsh Aggarwal <haaggarwal@nvidia.com>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: slangbot <ellieh+slangbot@nvidia.com>
Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>

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