RFR: 8316755: GenShen: Serviceability needs to know about ShenandoahGenerationalHeap [v2]

[William Kemper]

> Plumb `ShenandoahGenerationalHeap` into `vmStructs`.  
> 
> Testing: 
> 
> make test TEST=hotspot_serviceability TEST_VM_OPTS="-Xlog:gc*=info:file=/tmp/servicability.log -XX:+UseShenandoahGC -XX:+UnlockExperimentalVMOptions -XX:ShenandoahGCMode=generational" CONF=fastdebug
> 
> ...
> 
> Test results: passed: 319; failed: 0

William Kemper has updated the pull request incrementally with two additional commits since the last revision:

 - Fix copyright comment
 - Add missing newline

-------------

Changes:
  - all: https://git.openjdk.org/shenandoah/pull/329/files
  - new: https://git.openjdk.org/shenandoah/pull/329/files/2e30feea..0baf1a16

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=329&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=329&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/shenandoah/pull/329.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/329/head:pull/329

PR: https://git.openjdk.org/shenandoah/pull/329