[clang] [CIR] Upstream cir-canonicalize pass (PR #131891)

[Erich Keane via cfe-commits]

================
@@ -11,6 +11,24 @@
 
 include "mlir/Pass/PassBase.td"
 
+def CIRCanonicalize : Pass<"cir-canonicalize"> {
+  let summary = "Performs CIR canonicalization";
+  let description = [{
+    Perform canonicalizations on CIR and removes some redundant operations.
+
+    This pass performs basic cleanup and canonicalization transformations that
+    hopefully do not affect CIR-to-source fidelity and high-level code analysis
+    passes too much. Example transformations performed in this pass include
+    empty scope cleanup, trivial try cleanup, redundant branch cleanup, etc.
----------------
erichkeane wrote:

```suggestion
    empty scope cleanup, trivial `try` cleanup, redundant branch cleanup, etc.
```

https://github.com/llvm/llvm-project/pull/131891