Fix printer icon button background.

Swap hard-coded color values for dynamic theme values to correctly
handle dark and light mode swaps from the platform.

After - http://screen/4GmeprtHk8s5Sdb
Before - http://screen/6GgzEhBowkTwy3j

Test: Manual - see screenshots
Flag: com.android.printspooler.flags.printer_button_contrast
BUG: 341591022

Change-Id: Ifbf1df449ee4bc6953f51f2c9fc4899a85869469