Backport of d9fed5381a78c19ce14ddc8b9233f60d53c65453
Before this commit, when opening the calendar view with a specific locale
in the "week" view
the days were translated but the date format was wrong and fell back to english
This was because the translated terms were passed explicitly, but the locale did not
get passed
After this commit, we do what it takes to pass the locale to fullcalendar
and the dates are formatted with the right pattern
Also, there may be a bug in fullcalendar, because just passing the locale in the options
won't work, it should be instanciated first in fullcalendar's "locales cache"
OPW 1922092
OPW 1934127
closesodoo/odoo#30909