[FIX] web_editor: allow deleting all images in table cells

Before this commit, it was impossible to delete an image which was a
direct child of a table cell using the trash-icon button in the
toolbar.

This commit fixes the behavior by changing the logic quite a lot, so
it is kinda tricky (see https://github.com/odoo/odoo/commit/25849e918651eba080dac3af4e4fcdc8f1280241
for more explaination).

Closes https://github.com/odoo/odoo/issues/22523

addons/web_editor/static/src/js/summernote.js

@@ -1313,7 +1313,7 @@ function summernote_keydown_clean (field) {
 
 function remove_table_content(r) {
     var ancestor = r.commonAncestor();
-    var nodes = dom.listBetween(r.sc, r.ec);
+    var nodes = dom.listBetween(r.sc, r.ec, r.so, r.eo);
     if (dom.isText(r.sc)) {
         r.sc.textContent = r.sc.textContent.slice(0, r.so);
     }