Add maximise widget functionality (#7098)

Co-authored-by: J. Ryan Stinnett <jryans@gmail.com>

res/css/structures/_LeftPanelWidget.scss

@@ -134,7 +134,7 @@ limitations under the License.
             mask-position: center;
             mask-size: contain;
             mask-repeat: no-repeat;
-            mask-image: url('$(res)/img/feather-customised/maximise.svg');
+            mask-image: url("$(res)/img/element-icons/maximise-expand.svg");
             background: $muted-fg-color;
         }
     }

res/css/structures/_MainSplit.scss

@@ -23,9 +23,8 @@ limitations under the License.
 }
 
 .mx_MainSplit > .mx_RightPanel_ResizeWrapper {
-    padding: 5px;
-    // margin left to not allow the handle to not encroach on the space for the scrollbar
-    margin-left: 8px;
+    // no padding on the left. The spacing is taken care of by the main split content.
+    padding: 5px 5px 5px 0px;
     height: calc(100vh - 51px); // height of .mx_RoomHeader.light-panel
 
     &:hover .mx_RightPanel_ResizeHandle {

res/css/structures/_RightPanel.scss

@@ -22,7 +22,7 @@ limitations under the License.
     display: flex;
     flex-direction: column;
     border-radius: 8px;
-    padding: 8px 0;
+    padding: $container-border-width 0;
     box-sizing: border-box;
     height: 100%;
     contain: strict;