[FIX] web_editor: properly apply alignment to links

When the selection was in a link, the alignment buttons didn't work.
That is because they are supposed to align the parent paragraph, which
is temporarily in a contenteditable=false context when the selection is
in a link. This restores the context before applying an editor command,
and restores it afterwards.

task-3083748

Part-of: odoo/odoo#106772