[release/8.0-staging] Fix loop hoist memory-dependence tracking (#122057)

Port the .NET 9 fix in `optRecordLoopMemoryDependence` so that memory
dependencies coming from nested loops are recorded against the closest
ancestor loop that contains the consuming tree, rather than being
silently discarded.

Without this fix, when the loop hoister considers an IND whose value VN
has been folded to a constant via VN's MapStore/MapSelect machinery, the
`IsTreeLoopMemoryInvariant` check finds no entry in
`NodeToLoopMemoryBlockMap` and returns `true` vacuously. The IND is
then relocated to the loop preheader where it loads a stale value
instead of the post-store value the VN-folded constant represents.

Example pattern from the linked issue:

```csharp
for (sbyte i = -126; i > -128; i--)
{
    for (byte j = 2; j > 0; j--)
    {
        s_rt.Checksum(""c_0"", var4);   // virtual call inside inner loop
    }
    s_2 = 1;
    s_2 = s_2--;                        // hoisted IND reads stale s_2
}
```

Fix: walk up the parent chain of the update loop until one is found
that contains the tree's block (the .NET 9 `FlowGraphNaturalLoops`
version generalizes this; the 8.0 port uses `optLoopTable[..].lpParent`).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: AndyAyersMS

src/coreclr/jit/optimizer.cpp

@@ -7150,14 +7150,21 @@ void Compiler::optRecordLoopMemoryDependence(GenTree* tree, BasicBlock* block, V
         updateLoopNum = updateParentLoopNum;
     }
 
-    // If the update block is not the header of a loop containing
-    // block, we can also ignore the update.
+    // If the memory definition is part of an ancestor loop of `loopNum` then
+    // `tree` depends on memory defined in that ancestor loop. Walk up the parent
+    // chain of `updateLoopNum` looking for such an ancestor. Otherwise ignore
+    // the update.
     //
-    if (!optLoopContains(updateLoopNum, loopNum))
+    while ((updateLoopNum != BasicBlock::NOT_IN_LOOP) && !optLoopContains(updateLoopNum, loopNum))
     {
-        JITDUMP("      ==> Not updating loop memory dependence of [%06u]/" FMT_LP ", memory " FMT_VN "/" FMT_LP
-                " is not defined in an enclosing loop\n",
-                dspTreeID(tree), loopNum, memoryVN, updateLoopNum);
+        updateLoopNum = optLoopTable[updateLoopNum].lpParent;
+    }
+
+    if (updateLoopNum == BasicBlock::NOT_IN_LOOP)
+    {
+        JITDUMP("      ==> Not updating loop memory dependence of [%06u]/" FMT_LP ", memory " FMT_VN
+                " is not dependent on an ancestor loop\n",
+                dspTreeID(tree), loopNum, memoryVN);
         return;
     }