[IMP] web: avoid control panel height flickering

Before this commit, control panel height flickered when the
bottom bar only contained the pager (no view switcher and no
action buttons): when the user added a filter matched by no
record, the pager disappeared and the bottom bar height went from
35px to 30px.

To reproduce the issue, go to Data Cleaning (have some data), and
add a filter.

This commit reworks a bit the control panel layout such that the
bottom bar always keeps the same height.

task-2178933

closes odoo/odoo#46117

Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>

addons/web/static/src/scss/base_settings.scss

@@ -24,7 +24,6 @@
         .o_panel {
             display: flex;
             flex-flow: row wrap;
-            margin-bottom: $o-sheet-vpadding*0.5;
             width: 100%;
 
             .title, .o_setting_search {
@@ -54,7 +53,7 @@
 
         .o_form_statusbar {
             padding: 0;
-            margin: 0;
+            margin: 5px 0px;
             border: 0;
 
             .btn-primary, .btn-link  {

addons/web/static/src/scss/control_panel.scss

@@ -1,13 +1,14 @@
 
 .o_control_panel {
     border-bottom: 1px solid darken($o-control-panel-background-color, 20%);
-    @include o-webclient-padding($top: 10px, $bottom: 10px);
+    @include o-webclient-padding($top: 5px, $bottom: 5px);
     background-color: $o-control-panel-background-color;
 
     > div {
         display: flex;
         justify-content: space-between;
         min-height: 30px;
+        margin: 5px 0px;
     }
 
     .breadcrumb, .o_cp_left {
@@ -43,7 +44,6 @@
     .o_cp_left {
         display: flex;
         justify-content: space-between;
-        margin-top: 5px;
 
         > .o_cp_sidebar {
             padding-right: 10px;
@@ -76,7 +76,6 @@
 
     .o_cp_right {
         display: flex;
-        margin-top: 5px;
 
         > .o_cp_pager {
             margin: auto 0 auto auto;