[llvm] [SandboxIR] Preserve the order of switch cases after revert. (PR #115577)

[via llvm-commits]

vporpo wrote:

This solution is still implementation dependent given the lack of an addCase() API call with index. Not sure if I prefer this one over the previous one, given that the previous one was a constant-time operation.

https://github.com/llvm/llvm-project/pull/115577