Support multiple requiredSystemProperty in overlay

As-is: Only one requiredSystemProperty is allowed
To-be: It supports several requiredSystemProperty

Here is format for multiple fields.
  android:requiredSystemPropertyName="rw.num,rw.char"
  android:requiredSystemPropertyValue="1,a"

Test: m
Test: Make two overlay with different condition
      Check if it works properly depending on condition
      If there is no overlay package matching the condition, both aren't
      applied

Bug: 137628879
Change-Id: I4c8c4a1304dc52d6568767d90e3dcbf6acef024a