Linalg portion of the tutorial - part 3

    This CL starts the third part of the Linalg tutorial by adding support for ops to declare how they lower themselves to other ops.
    Tests are added that demonstrate matmul lowering to a loop over matvec and matvec lowering to a loop over dot.

    This is part of a list of CLs that add new Transforms and Analyses to Linalg3: it iseasier to integrate in small chunks.

    As part of working with the TensorContractionBase template class and in an effort to add pieces incrementally without copying code, it is easiest to define operations ahead of time in Linalg2/TensorOps.h and gradually implement them as needed. This CL performs the necessary refactoring for this to happen.

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PiperOrigin-RevId: 241605869