RFR: 8266740: Shenandoah: Heap region count calculation still wrong after JDK-8265239

[Zhengyu Gu]

JDK-8265239 only addressed heap size that needed to be aligned to region size, it did not address the adjustment needed when use large page.

To avoid all the complication, I purpose to defer region count calculation until heap size adjustment is done.

Test:
- [x] hotspot_gc_shenandoah
- [x] runtime/os/TestTracePageSizes.java now passed

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Commit messages:
 - Merge branch 'master' into JDK-8266740-region-count-2
 - v1

Changes: https://git.openjdk.java.net/jdk/pull/3922/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3922&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266740
  Stats: 15 lines in 3 files changed: 9 ins; 5 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3922.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3922/head:pull/3922

PR: https://git.openjdk.java.net/jdk/pull/3922