NFC: Standardize the terminology used for parent ops/regions/etc.

There are currently several different terms used to refer to a parent IR unit in 'get' methods: getParent/getEnclosing/getContaining. This cl standardizes all of these methods to use 'getParent*'.

PiperOrigin-RevId: 262680287
diff --git a/mlir/lib/Dialect/LoopOps/LoopOps.cpp b/mlir/lib/Dialect/LoopOps/LoopOps.cpp
index 63e0da0..13dc35e 100644
--- a/mlir/lib/Dialect/LoopOps/LoopOps.cpp
+++ b/mlir/lib/Dialect/LoopOps/LoopOps.cpp
@@ -118,7 +118,7 @@
   if (!ivArg)
     return ForOp();
   assert(ivArg->getOwner() && "unlinked block argument");
-  auto *containingInst = ivArg->getOwner()->getContainingOp();
+  auto *containingInst = ivArg->getOwner()->getParentOp();
   return dyn_cast_or_null<ForOp>(containingInst);
 }