Rename pressure ionization to IPD ionization

[BrianMarre]

Renames pressureIonization to ipdIonization(Ionization Potential Depression ionization) in preparation for the implementation of BSI based IPD models.

This naming generalization is necessary to avoid confusion, since both BSI and pressure ionization will use the same infrastructure.

• [x] requires PR #5100 to be merged first
• [x] requires PR #5120 to be merged first

Attention: This PR breaks old simulation setups using a non default atomicPhysics_Debug.param. To fix your setup replace in atomicPhysics_Debug.param the following block:

    namespace kernel::applyPressureIonization
    {
        //! @attention performance relevant
        constexpr bool ELECTRON_PARTICLE_BOX_FILL_GAPS = <UserSetting>;
    } // namespace kernel::applyPressureIonization

with the following

    namespace kernel::applyIPDIonization
    {
        //! @attention performance relevant
        constexpr bool ELECTRON_PARTICLE_BOX_FILL_GAPS = <UserSetting>;
    } // namespace kernel::applyIPDIonization

Take care to replace <UserSetting> with the previous setting.

[psychocoderHPC]

@BrianMarre can be rebased