[TableGen] Allow additional result patterns not directly used for replacement

    This CL looses the requirement that all result patterns in a rewrite rule must
    replace a result of the root op in the source pattern. Now only the last N
    result pattern-generated ops are used to replace a N-result source op.

    This allows to generate additional ops to aid building up final ops used to
    replace the source op.

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PiperOrigin-RevId: 241783192