Hide Memory usage UI fields if flag is enabled

This change updates the Memory use UI in developer settings to hide
memory fields by default if the AppProfiler PSS deprecation flag is
enabled. A toggle is provided to resume PSS profiling and reinstate the
memory fields, and shows a dialog to reboot if the toggle is updated.

The summary for the "Memory" button in developer settings will show
"Memory profiling disabled" instead of "Avg X GB of Y memory used" if
PSS profiling is not enabled.

Test: With the flag enabled, flash and verify that:
      - The memory fields are hidden by default, and the summary shows
	the expected "Memory profiling disabled" text
      - Clicking the toggle shows the reboot dialog, which will
	correctly change the setting and reboot if accepted, and keep
	the setting and not reboot if denied
      - Check that AppProfiler correctly profiles PSS or RSS based on
	the state of the toggle, which persists across reboots
      - Included UI test for Memory page elements based on flag value.
Bug: 296454553
Change-Id: Ie21791502445a321446cb8110e5800089f47ac58