[TableGen] Support multiple variadic operands/results

    Certain ops can have multiple variadic operands/results, e.g., `tf.DynamicStitch`.
    Even if an op has only one variadic operand/result, it is not necessarily the
    very last one, e.g., `tf.RaggedGather`. This CL enhances TableGen subsystem to be
    able to represent such cases.

    In order to deduce the operand/result value range for each variadic operand,
    currently we only support variadic operands/results all of the same size.
    So two new traits, `SameVariadicOperandSize` and `SameVariadicResultSize` are
    introduced.

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PiperOrigin-RevId: 245310628