[FIX] web_editor: list indentation in table

Before this commit:

Indenting list using tab inside a table used to switch to the next cell.

After this commit:

Indenting list using tab inside a table now indents a list instead of switching
to the next cell.

task-3470092

closes odoo/odoo#132508

Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>