Before this commit, the widget's description was stored on the
component and this component was then registered.
Now, an object describing the widget is used on registration the same way
as it is done for views since b828cfc.
This split the component's description (props, template, ...) of
the widget's description ( component, extractProps, ...) and makes
it clearer.
We did the same thing for fields in 9f4622492c
Part of task: 3179751
closesodoo/odoo#112962
Related: odoo/enterprise#37215
Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>