When exporting a grouped list view with some nested groups, the aggregate value
of parent groups are not correct. It always sums aggregated values of children
whether the group operator is 'sum' or not (could be 'max', 'avg', ...).

This behavior is wrong and can even lead to a crash if the aggregated field is a
date field (e.g. with group_operator='max'). (Try two sum two dates...)

The quick fix 85cf47f was merged just before OXP to avoid any crash. This fix
limited the support of aggregates to only int and float fields.
This commit remove this limitation.

This commit correclty implements the aggregation for parent group for all
field types and all group_operator.

This commit also improves the export feature tests.

X-original-commit: 5e7e4fa98698967e3c4fd0903f4aa8e91981a6cd

PURPOSE
=======

Add the support of grouped exports.
Allow the user to export all records in one click from
the listview, without having to go through the export modal,
taking into account the domain, groupbys, and visible fields.

SPECIFICATION
=============

When exporting (whether it is from the modal or from the shortcut),
any groupby(s) set on the listview should be taken into account (all unfolded)
- UNLESS the export is import-compatible
- each subgroup header has an indentation compared to its parent
- the 'group headers' in the exported file should contain the
  same info (label, field aggregates) as it has in the listview.

New secondary button on the tree view with label 'EXPORT' (to be confirmed...)
- the export shortcut disregard the selected records, it exports all records
  according to the domain.
- the button is visible even if there is no selected records.
- essentially the export shortcut does the same thing as the following:
    - select all records
    - hit 'action' then 'export'
    - hit 'export'

Define a boolean attribute on <tree> to specify whether or not the export shortcut should be displayed

Task 2072910