[MM-61582][MM-61605][MM-61622][MM-63029][MM-63026][MM-63059] Mobile View accessibility fixes (#31328)

* [MM-61582] Ensure textbox changes size when the window is too small

* [MM-61605] Fix clipping on menu modal in mobile view

* [MM-61622] Make mobile view RHS scrollable

* [MM-63029] Fix mobile view Browse Channels modal arrangement

* [MM-63026] Make new channel body scrollable if needed, flex to full screen on mobile view

* [MM-63059] Make Settings Modal properly responsive with flexbox for mobile view

* Fix lint

* [MM-64033] Fix mobile view for User Groups, another fix for Browse Channels

* Fix notification modal

* PR feedback

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

webapp/platform/components/src/generic_modal/generic_modal.scss

@@ -137,13 +137,13 @@
                 }
             }
         }
+    }
 
-        @media screen and (max-width: 640px) {
-            margin: 0 !important;
+    @media screen and (max-width: 640px) {
+        margin: 0 !important;
 
-            .modal-header {
-                box-shadow: var(--elevation-2);
-            }
+        .modal-header {
+            box-shadow: var(--elevation-2);
         }
     }