This commit adds a new Unselect all button displayed when at least two
records are selected in a list view. This button appears near other list
buttons. Once clicked, the selected items are deselected and the button
disappears.
Some list view tests have been modified since that change now adds a
button in cases where it was not expected before. Those tests now verify
the behavior when the button is clicked.
task-3081101
closesodoo/odoo#107294
Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>