[FIX] web: export of id from grouped elements does not fail

Steps to reproduce:
- install sales
- go to sales > go to any list view (SO for example) and group by
anything (customer for example)
- click on action > export > add ID to the exported columns
- click export

Previous behavior:
you get a traceback: "Invalid field specification '.id'."

Current behavior:
ids are exported as intended

opw-2194233

closes odoo/odoo#48222

X-original-commit: c8217080d960ec3f8436111ce60a17754fe64f2d
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>
Signed-off-by: mightyjol <jhk-odoo@users.noreply.github.com>

addons/web/controllers/main.py

@@ -660,6 +660,8 @@ class GroupsTreeNode:
         """ Return field names of exported field having a group operator """
         aggregated_field_names = []
         for field_name in self._export_field_names:
+            if field_name == '.id':
+                field_name = 'id'
             if '/' in field_name:
                 # Currently no support of aggregated value for nested record fields
                 # e.g. line_ids/analytic_line_ids/amount
@@ -1857,7 +1859,7 @@ class ExportFormat(object):
         if not import_compat and groupby:
             groupby_type = [Model._fields[x.split(':')[0]].type for x in groupby]
             domain = [('id', 'in', ids)] if ids else domain
-            groups_data = Model.read_group(domain, field_names, groupby, lazy=False)
+            groups_data = Model.read_group(domain, [x if x != '.id' else 'id' for x in field_names], groupby, lazy=False)
 
             # read_group(lazy=False) returns a dict only for final groups (with actual data),
             # not for intermediary groups. The full group tree must be re-constructed.