No functional changes.
Merge the modal callbacks of the `VIEW3D_OT_move`, `VIEW3D_OT_rotate` and `VIEW3D_OT_zoom` operators into a single simplified `view3d_navigate_modal_fn` callback.
Deduplicates initialization, finalization and `event_code` code.
Improved support for operation switching by existing (but unmapped) modal keymap items `VIEWROT_MODAL_SWITCH_ZOOM`, `VIEWROT_MODAL_SWITCH_MOVE` and `VIEWROT_MODAL_SWITCH_ROTATE`.