Fix kyaml merge2: $patch directives ignored with ListPrepend

[saitejabandaru-in]

Fixes #6146.

When using merge2.MergeStrings with ListIncreaseDirection: MergeOptionsListPrepend, strategic merge patch directives ($patch: replace, $patch: delete) on individual list elements were silently ignored.

The root cause was in kyaml/yaml/walk/associative_sequence.go where appendListNode(itemsToBeAdded, dest, ...) was called. Because dest contained the original unmerged items, appending dest into itemsToBeAdded (which contained the correctly merged items) caused the merged elements to be overwritten by the original elements.

This fix properly updates dest with itemsToBeAdded (the merged items) first so that the patches are applied. Then it applies the fully patched dest to itemsToBeAdded to correctly prepend the new items while retaining the patch updates.

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