fix(expansion-panel): wrong margins in rtl (#5800)

Author: crisbeto

src/lib/expansion/expansion-panel-header.scss

@@ -32,16 +32,20 @@ $mat-expansion-panel-header-height-expanded: 64px;
   overflow: hidden;
 }
 
-.mat-expansion-panel-header-title {
+.mat-expansion-panel-header-title,
+.mat-expansion-panel-header-description {
   display: flex;
   flex-grow: 1;
   margin-right: 16px;
+
+  [dir='rtl'] & {
+    margin-right: 0;
+    margin-left: 16px;
+  }
 }
 
 .mat-expansion-panel-header-description {
-  display: flex;
   flex-grow: 2;
-  margin-right: 16px;
 }
 
 /**

src/lib/expansion/expansion-panel.scss

@@ -29,5 +29,10 @@
 
   button.mat-button {
     margin-left: 8px;
+
+    [dir='rtl'] & {
+      margin-left: 0;
+      margin-right: 8px;
+    }
   }
 }