[FIX] web_editor: properly handle deleteRange where tables are involved

Tables have their own custom selection in Odoo Editor, so rectangular
cell selection is supported. Selecting a whole row/column/table then
pressing delete/backspace removes the whole row/column/table. But just
selecting some cells should only empty them, which we failed to do,
resulting sometimes in broken tables.

The code to remove selected rows/columns/table was triggered when
pressing backspace/delete, which failed to account for cases where we
need to delete the range without pressing those keys (for instance when
typing a character). This moves that code to `deleteRange` so as to make
it the standard behavior when deleting a range that includes table
cells.

task-3032817

Part-of: odoo/odoo#104285