PURPOSE
The attachment icon in the chatter is too discrete, a lot of users easily miss
it.
SPECIFICATIONS
- Allow for file upload through drag and drop and the whole chatter.
It doesn't matter whether the file tray is unfolded.
Hence, removed DropZone on attachmentBox as now have DropZone on
the whole chatter.
- On the file tray, rename "Attachments" to "Files" and
"Add attachments" to "Attach files".
- When there are files attached to the record, display "X files".
- when there is no file yet, display 'Attach files'. Although clicking on it
opens the file explorer, but doesn't unfold the tray yet. Once the file is
submitted, the file tray unfolds to show confirmed upload to the user.
Task-2413814
closesodoo/odoo#91335
Related: odoo/enterprise#27763
Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>