RFR: Generation affiliation transitions for heap regions. [v3]

[Bernd Mathiske]

> Preparatory renaming generation->affiliation since we will want to have a class called ShenandoahGeneration that is not an enum. The next PR will build on this. It will be a big refactoring that pulls code out of the ShenandoahHeap class and puts it into generation-specific classes that are subclasses of ShenandoahGeneration.
> 
> The Affiliation declaration still sits in AllocRequest and not in ShenandoahHeapRegion or ShenandoahGeneration for the same reason as before: it is hard to get anything to compile in other combinations of what goes where. I tried.
> 
> The card table update code in the set_affiliation() will be revised and augmented later, but seems OK as a first step.

Bernd Mathiske has updated the pull request incrementally with one additional commit since the last revision:

  Add missing precomiled header include for Windows builds.

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Changes:
  - all: https://git.openjdk.java.net/shenandoah/pull/7/files
  - new: https://git.openjdk.java.net/shenandoah/pull/7/files/dadb608e..131a8b3b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=7&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=7&range=01-02

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/shenandoah/pull/7.diff
  Fetch: git fetch https://git.openjdk.java.net/shenandoah pull/7/head:pull/7

PR: https://git.openjdk.java.net/shenandoah/pull/7