[FIX] web: restore form and chatter width size

In 15.3, the width was applied on `o_form_sheet_bg`.
As the form view has been refactored in 16, we have to apply
it on the new parent `o_form_view_container`.

We also restore the chatter width to the same value as in 15.3:
```scss
.o_FormRenderer_chatterContainer {
    &.o-aside {
        width: $o-chatter-min-width;
    }
}
```

Steps to reproduce:
- Open Helpdesk on screen at 1534x657
- Open a vip support
- Unfold 'Done'
- Click on 'Ugly Chair', the chatter take a lot of space => bug

Steps to reproduce
- Open Sales
- Open a quotation
- Switch between Order lines, Other info, Customer Signature
  notebook tabs a flicker occurs => bug

closes odoo/odoo#102781

Signed-off-by: Adrien Dieudonné (adr) <adr@odoo.com>

addons/mail/static/src/widgets/form_renderer/form_renderer.scss

@@ -20,8 +20,7 @@
         border-left: $border-width solid;
         padding: map-get($spacers, 0);
         max-width: var(--Chatter-max-width);
-        min-width: $o-chatter-min-width;
-        width: auto;
+        width: $o-chatter-min-width;
 
         .o_Message.o-not-discussion {
             border-width: $border-width 0;

addons/web/static/src/views/form/form_controller.scss

@@ -1106,9 +1106,12 @@
 .o_form_view.o_xxl_form_view {
     flex-flow: row nowrap !important;
 
+    .o_form_view_container {
+        width: $o-form-sheet-min-width + 2 * $o-horizontal-padding;
+    }
+
     .o_form_sheet_bg {
         flex: 1 1 auto; // Side chatter is disabled if this has to shrink but this was added for safety
-        // max-width: map-get($container-max-widths, xl) + 2 * $o-horizontal-padding; // would be logical but breaks no-chatter form views
         padding: 0 $o-horizontal-padding;
         overflow: auto;
         border-bottom: none;