[FIX] web_editor: fix HTML/CSS editor resizing bug

Starting on version 16.0, the HTML/CSS editor is very hard to resize.
This is due to 16.0 introducing an iframe for the website: as soon as
your mouse enters the iframe, the editor loses focus and cannot be
resized anymore.
This commit fixes that.

task-3006138

closes odoo/odoo#120729

X-original-commit: e489abeffc72293544acb18eba23b52ed2224d60
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

addons/web_editor/static/src/js/common/ace.js

@@ -338,10 +338,12 @@ var ViewEditor = Widget.extend({
         function startResizing(e) {
             refX = e.pageX;
             resizing = true;
+            document.body.classList.add("o_ace_view_editor_resizing");
         }
         function stopResizing() {
             if (resizing) {
                 resizing = false;
+                document.body.classList.remove("o_ace_view_editor_resizing");
 
                 if (this.errorSession) {
                     // To trigger an update of the error display

addons/web_editor/static/src/scss/web_editor.common.scss

@@ -485,6 +485,10 @@ a.o_underline {
     }
 }
 
+.o_ace_view_editor_resizing iframe {
+    pointer-events: none;
+}
+
 .o_ace_error_popover {
     max-width: 40vw;