Add a global setting for forcing PSS collection

The flag for replacing PSS collection in AppProfiler with RSS will make
numbers in the "Memory use" UI in developer settings incorrect, as the
numbers presented there are gathered from AppProfiler. This change adds
a global setting that can be toggled from that page to resume collecting
PSS information.

Test: Build+flash, verify using test logs that PSS is collected in
      AppProfiler instead of RSS when the new toggle in Settings is
      enabled while the flag is enabled.
Bug: 296454553
Change-Id: Ic821a6fc9dbb6bd2c1a5d2c66805d8e9be70fae7