Linalg portion of the tutorial - part 3-2

    This CL adds support for lowering tensor contractions to loops declaratively.
    This is done thanks to two properties of the such operations:
    1. the definition of an AffineMap getLoopsToOperandRangesMap for each op which maps iteration space dimensions to ranges of the view operands, in their order of occurrence;
    2. the definition of a scalar implementation for each op which creates the computation inside the loops given enclosing parallel and reduction loops,

    All the other properties are derived in a generic fashion from these 2 properties and a few analyses.

    A lowerToLoops transformation is added as well as a test that exercises it.

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PiperOrigin-RevId: 241783992