feat(material/slider): show background-color in print stylesheet (#11364)

* added color-adjust to mat-slider-wrapper to display slider correctly while printing

Author: Felix

src/material/slider/_slider-theme.scss

@@ -49,6 +49,11 @@
     theming.get-color-from-palette($foreground, base, $mat-slider-tick-opacity);
   $mat-slider-tick-size: 2px;
 
+  .mat-slider-wrapper {
+    -webkit-print-color-adjust: exact;
+    color-adjust: exact;
+  }
+
   .mat-slider-track-background {
     background-color: $mat-slider-off-color;
   }