[llvm] AMDGPU: Add more tests for fmed3 instcombine folds (PR #139529)

[Matt Arsenault via llvm-commits]

arsenm wrote:

* **#139531** <a href="https://app.graphite.dev/github/pr/llvm/llvm-project/139531?utm_source=stack-comment-icon" target="_blank"><img src="https://static.graphite.dev/graphite-32x32-black.png" alt="Graphite" width="10px" height="10px"/></a>
* **#139530** <a href="https://app.graphite.dev/github/pr/llvm/llvm-project/139530?utm_source=stack-comment-icon" target="_blank"><img src="https://static.graphite.dev/graphite-32x32-black.png" alt="Graphite" width="10px" height="10px"/></a>
* **#139529** <a href="https://app.graphite.dev/github/pr/llvm/llvm-project/139529?utm_source=stack-comment-icon" target="_blank"><img src="https://static.graphite.dev/graphite-32x32-black.png" alt="Graphite" width="10px" height="10px"/></a> 👈 <a href="https://app.graphite.dev/github/pr/llvm/llvm-project/139529?utm_source=stack-comment-view-in-graphite" target="_blank">(View in Graphite)</a>
* `main`


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https://github.com/llvm/llvm-project/pull/139529