Fix crash in state reconciliation

Summary:
Changelog: [internal]

Repro steps:

1. Go to fbsource/fbobjc.
2. Run following focus command P124860753.
3. Enable Address Sanitizer in Xcode.
3. Run the app from Xcode.
5. Make sure `react_fabric.enable_marketplace_home_ios` and `react_fabric.enabled_state_reconciliation_ios` Mobile Config flags are set to true.
6. Navigate to Marketplace Home and observe use of freed memory exception. You have to wait until second page of marketplace home feed is loaded.

{F228880980}

# Root cause

`ChangedShadowNodePairs` being a vector of pairs of references.
Those `shared_ptr` do not outlive the the run of `reconcileStateWithTree` (that's what I originally thought when I made them references).

This was introduced in D19814500.

Reviewed By: JoshuaGross

Differential Revision: D19977784

fbshipit-source-id: 8c4a381137baa08a6af9d3c1cb295fe6c2b2bf95

ReactCommon/fabric/mounting/TreeStateReconciliation.cpp

@@ -10,8 +10,8 @@
 namespace facebook {
 namespace react {
 
-using ChangedShadowNodePairs = std::vector<
-    std::pair<ShadowNode::Shared const &, ShadowNode::Unshared const &>>;
+using ChangedShadowNodePairs =
+    std::vector<std::pair<ShadowNode::Shared, ShadowNode::Unshared>>;
 
 /**
  * Clones any children in the subtree that need to be cloned, and adds those to