Force tablet view on Collaboration page

refs VICE-4747

flag = instui_nav

Test plan:
- Navigate to the collaboration page
- Check the adding button in desktop and tablet view
- Button should be unter the title in tablet view
- Check with instui_nav feature flag as well

Change-Id: Iaef5c3ac492e0ddd4c7656f94be0dd15e34ed168
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/360523
Reviewed-by: Daniel Matyas Vincze <daniel.vincze@instructure.com>
QA-Review: Dora Csolakov <dora.csolakov@instructure.com>
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Product-Review: Tamás Balogh <tamas.balogh@instructure.com>

app/stylesheets/base/_shared.scss

@@ -1,7 +1,8 @@
 @import "mixins/typography";
 
 @mixin page_header_container {
-  margin-bottom: 36px;display: flex;
+  display: flex;
+  margin-bottom: 36px;
   justify-content: space-between;
   align-items: center;
   flex-wrap: wrap;

app/stylesheets/base/mixins/_breakpoints.scss

@@ -31,6 +31,9 @@
   @else if $breakpoint == desktop {
     $dimension: 992px;
   }
+  @else if $breakpoint == ICEDesktop {
+    $dimension: 1025px;
+  }
   @else if $breakpoint == desktop--nav-open {
     $dimension: 1140px;
   }

app/stylesheets/components/_g_collaborations.scss

@@ -20,21 +20,25 @@ $dark-blue: #edf4fc;
 $green: #f5fbf7;
 $highlight-blue: #00b5fe;
 
-.collab-page_header {
-  @include page_header;
-}
 
 .page_header_container {
   @include page_header_container;
-}
+  align-items: flex-start;
+  flex-direction:  column;
+  @include breakpoint(ICEDesktop) {
+    flex-direction: row;
+  }
+  .collab-page_header {
+    @include page_header;
+  }
 
-.actions_buttons-container {
-  @include action_buttons_container;
+  .actions_buttons-container {
+    @include action_buttons_container;
+  }
 }
 
-
 .collaborations-header {
-  display: block;
+  display: flex;
   overflow: hidden;
   margin-bottom: 14px;