[FIX] hr_timesheet: Widget for planned hours

Before this commit:
The field `planned_hours` and `subtask_planned_hours` are present
twice. This causes problems with widget: different widgets are put
on different fields, but only the last on was put on all of them.
Code to edit label with hours/days is not flexible, we need to
write each possibilities.

After this commit:
All fields are present only once in the view. A new widget is
created to manage days with a factor. In this new widget, instead
of having a toggle button, we can insert a float.
When the widget timesheet_uom is set on a field, we modify his string
with hours/days.

closes odoo/odoo#56702

Taskid: 2326216
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>