Connect pairs on both sides so we can get to the other pair from either state

This doesn't matter for CommitViewTransitions since we only read on one side
but it matters for ApplyGesture when we read on the reverse end.

Author: sebmarkbage

packages/react-reconciler/src/ReactFiberApplyGesture.js

@@ -152,6 +152,7 @@ function trackDeletedPairViewTransitions(deletion: Fiber): void {
               // The "new" instance is the already mounted one we're deleting.
               const newInstance: ViewTransitionState = child.stateNode;
               oldInstance.paired = newInstance;
+              newInstance.paired = oldInstance;
               const clones = oldInstance.clones;
               if (clones !== null) {
                 // If we have clones that means that we've already visited this
@@ -201,6 +202,7 @@ function trackEnterViewTransitions(deletion: Fiber): void {
         // The "new" instance is the already mounted one we're deleting.
         const newInstance: ViewTransitionState = deletion.stateNode;
         oldInstance.paired = newInstance;
+        newInstance.paired = oldInstance;
         const clones = oldInstance.clones;
         if (clones !== null) {
           // If we have clones that means that we've already visited this

packages/react-reconciler/src/ReactFiberCommitViewTransitions.js

@@ -348,9 +348,10 @@ function commitDeletedPairViewTransitions(deletion: Fiber): void {
                 restoreViewTransitionOnHostInstances(child.child, false);
               } else {
                 // We'll transition between them.
-                const oldinstance: ViewTransitionState = child.stateNode;
+                const oldInstance: ViewTransitionState = child.stateNode;
                 const newInstance: ViewTransitionState = pair;
-                newInstance.paired = oldinstance;
+                newInstance.paired = oldInstance;
+                oldInstance.paired = newInstance;
                 // Note: If the other side ends up outside the viewport, we'll still run this.
                 // Therefore it's possible for onShare to be called with only an old snapshot.
                 scheduleViewTransitionEvent(child, props.onShare);
@@ -399,9 +400,10 @@ export function commitExitViewTransitions(deletion: Fiber): void {
       } else if (pair !== undefined) {
         // We found a new appearing view transition with the same name as this deletion.
         // We'll transition between them instead of running the normal exit.
-        const oldinstance: ViewTransitionState = deletion.stateNode;
+        const oldInstance: ViewTransitionState = deletion.stateNode;
         const newInstance: ViewTransitionState = pair;
-        newInstance.paired = oldinstance;
+        newInstance.paired = oldInstance;
+        oldInstance.paired = newInstance;
         // Delete the entry so that we know when we've found all of them
         // and can stop searching (size reaches zero).
         // $FlowFixMe[incompatible-use]: Refined by the pair.