Add host-side longevity library support.

Splits the existing device-side library, tests, and samples into a core
library that supports host-side testing and a device-side library that
extends and modifies the core library.

Bug: 69562941
Test: LongevityHostLibTests, LongevityPlatformLibTests
Change-Id: Ib3e5bdfb8e89793191793d4a031f82ae342b6e32