rts: eras profiling mode

The eras profiling mode is useful for tracking the life-time of
closures. When a closure is written, the current era is recorded in the
profiling header. This records the era in which the closure was created.

* Enable with -he
* User mode: Use functions ghc-experimental module GHC.Profiling.Eras to modify the era
* Automatically: --automatic-era-increment, increases the user era on major
  collections
* The first era is era 1
* -he<era> can be used with other profiling modes to select a specific
  era

If you just want to record the era but not to perform heap profiling you
can use `-he --no-automatic-heap-samples`.

https://well-typed.com/blog/2024/01/ghc-eras-profiling/

Fixes #24332