*:l10n_de_pos_cert,pos_iot

Previously, the point of sale and related modules made heavy usage of
`useListener`. This is because the pos was converted early to owl, and
in owl 1, using events to communicate between components was encouraged.

In owl 2, the decision was made to stop encouraging this way of
communicating between components, because it encourages communication
accross many layers of components, and is also hard to debug. In
addition, in owl 2, because components can have 0 or more than node,
including non HTMLElement nodes like text or comment nodes, owl removed
the implementation of useListener, as useListener relies on the presence
and unicity of a root HTMLElement per component on which we can attach
event listeners.

Another problem is that events rely on the fact that the components are
in the DOM so that the event can propagate, which can lead to issues in
some cases and in particular, in the PoS, if you load the point of sale
and switch tabs, some things will be broken because we are triggering
events, but there have not been any animation frame fired in the tab
because it's not focussed, and so owl has not mounted the component yet.
 
When migrating odoo to owl 2, we introduced a shim for this.el and
useListener in LegacyComponent, with the hope to remove it as soon as
possible.

This commit removes all usage of useListener from the pos modules for
those reasons. In some cases, useListener was incorrectly used intstead
of t-on, and the event was triggered and handled by the same component,
in other cases, a simple callback could be passed to a child component.
In a few cases, a method had to be implemented on the store as we wanted
this method to be available everywhere.

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