rts: Post ticky entry counts to the eventlog

The ticky-ticky profiler is a useful tool but provides little in the way of temporal resolution. In particular, benchmarks of the non-moving garbage collector has revealed what I believe to be a thunk leak in GHC when compiling Cabal's LicenseId module that I believe the ticky profiler would pin-point with temporal resolution.

This patch provides said resolution by giving the RTS the ability to periodically record samples of ticky counters to the eventlog.