[LinearAlgebra] CompressedRowSparseMatrixConstraint: make consistent the serialization/deserialization process

For now, the serialization of a CSR cannot be used a deserialization as the format are different. In a nutshell, it is not possible to do:

    std::ostringstream oss;
    oss << outMatrix;

    CSR inMatrix;
    std::istringstream iss(oss.str());
    iss >> inMatrix;

So this PR tries to fix it by changing the output format of the serialization. + more concise (faster to serialize, less space) - much less human-readable

Other/complimentary solutions: - adding a nice printing (same as the deserialization now) - dont change the serialization but the deserialization

EDIT:

restoration of the pretty output in a function (prettyPrint())
use this print in a specialization for its Qt Widget (so no change of behavior with the Qt GUI)

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it builds with SUCCESS for all platforms on the CI.
it does not generate new warnings.
it does not generate new unit test failures.
it does not generate new scene test failures.
it does not break API compatibility.
it is more than 1 week old (or has fast-merge label).

sofa-framework / sofa

[LinearAlgebra] CompressedRowSparseMatrixConstraint: make consistent the serialization/deserialization process #5087