fix(table,sort): incorrect spacing in rtl

Fixes a few instances in the `table` and `sort` modules where the spacings weren't being inverted in RTL layouts.

Author: crisbeto

src/lib/sort/sort-header.scss

@@ -34,11 +34,16 @@ $mat-sort-header-arrow-hint-opacity: 0.38;
   height: $mat-sort-header-arrow-container-size;
   width: $mat-sort-header-arrow-container-size;
   min-width: $mat-sort-header-arrow-container-size;
-  margin: 0 0 0 $mat-sort-header-arrow-margin;
   position: relative;
   display: flex;
 
-  .mat-sort-header-position-before & {
+  &,
+  [dir='rtl'] .mat-sort-header-position-before &{
+    margin: 0 0 0 $mat-sort-header-arrow-margin;
+  }
+
+  .mat-sort-header-position-before &,
+  [dir='rtl'] & {
     margin: 0 $mat-sort-header-arrow-margin 0 0;
   }
 }

src/lib/table/table.scss

@@ -33,10 +33,20 @@ $mat-row-horizontal-padding: 24px;
 
 .mat-cell:first-child, .mat-header-cell:first-child {
   padding-left: $mat-row-horizontal-padding;
+
+  [dir='rtl'] & {
+    padding-left: 0;
+    padding-right: $mat-row-horizontal-padding;
+  }
 }
 
 .mat-cell:last-child, .mat-header-cell:last-child {
   padding-right: $mat-row-horizontal-padding;
+
+  [dir='rtl'] & {
+    padding-right: 0;
+    padding-left: $mat-row-horizontal-padding;
+  }
 }
 
 .mat-cell, .mat-header-cell {