[views] simplify and fix the TreeView (closes #16055814) Simplify the (internal) TreeView._init_params() method to get rid of the useless 'initial_thru_ajax' argument. The ajax tree view was not working properly when loaded via ajax, for instance from a lazy tab. This was due to the buggy protection against double javascript/ css inclusion, which is no more needed server-side as it is now implemented client-side. Deprecate use of the initial_thru_ajax argument of the TreeView.call() method.

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