[IMP] web: Export grouped list view in xls file

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