Read RSS high watermark

The value is read from /proc/PID/status or memory.max_usage_in_bytes (for devices with per-app memcg enabled).

Reading the value takes about 2ms per process.
Full snapshot taken by statsd is around 300ms.

Results: https://docs.google.com/spreadsheets/d/1vG9ku8Uu8104CmKbO4cNeEKVeeByvHY--p0_dK1GAdA/edit?usp=sharing

Bug: 115477992
Test: atest FrameworksServicesTests
Change-Id: I87995cbd85085375ade685f29e986ba173f9693e