Load Flow Validation: add support for non-linear shunt compensators

[jeandemanged]

Describe the current behavior

In Load Flow Validation, an exception is thrown if the network contains non-linear shunt compensators

throw new PowsyblException("non linear shunt not supported yet")

Only workaround is to disable shunts validation

Describe the expected behavior

add support for non-linear shunt compensators in load flow validation

Describe the motivation

completeness

Extra Information

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