Adapt to the new possible Powsybl PhaseTapChanger regulation modes

[alicecaron]

Describe the current behavior

A PhaseTapChanger can have a FIXED_TAP RegulationMode regardless of its regulating value.

Describe the expected behavior

A PhaseTapChanger FIXED_TAP RegulationMode no longer exists. Instead the regulating boolean should be set to false to represent the old fixed tap mode.
So regulating attribute must be taken into account to determine if it is regulating, regardless its RegulationMode which must be set in any case as one of the following ones: CURRENT_LIMITER, ACTIVE_POWER_CONTROL.

Describe the motivation

Adapt to the powsybl-core#3344 issue that removes the FIXED_TAP regulation mode.

Extra Information

No response