[FIX] website: fix CSS for AceEditor

The use of AceEditor's CSS on "assets_backend" affects the editor widget
on fields.

The goal of this commit is to fix this behaviour by excluding form
fields.

See merge commit for more information.

task-2687506

addons/website/static/src/components/ace_editor/ace_editor.scss

@@ -1,4 +1,4 @@
-.o_ace_view_editor {
+.o_ace_view_editor:not(.oe_form_field) {
     @include o-position-absolute($o-navbar-height, 0, 0);
     position: fixed;
     z-index: $zindex-modal;