add css-containment to workspace variables

Author: aminya

static/core-ui/workspace-view.less

@@ -1,6 +1,8 @@
 @import "ui-variables";
+@import "utils";
 
 atom-workspace {
+  contain: @contain_all;
   display: flex;
   flex-direction: column;
   height: 100%;
@@ -11,17 +13,20 @@ atom-workspace {
   font-family: @font-family;
 
   atom-workspace-axis {
+    contain: @contain_but_layout_paint;
     position: relative;
   }
 
   atom-workspace-axis.horizontal {
+    contain: @contain_but_layout_paint;
     display: flex;
     flex: 1;
     min-width: 0;
     min-height: 0;
   }
 
   atom-workspace-axis.vertical {
+    contain: @contain_but_layout_paint;
     display: flex;
     flex: 1;
     flex-direction: column;