[jdk16u] RFR: 8266802: Shenandoah: Round up region size to page size unconditionally

[Zhengyu Gu]

I would like to backport this patch to 16u.

Without this patch, Shenandoah may not create enough regions to cover whole heap, that results some of heap memory never used.

The original patch applies cleanly to 16u and passed new test in patch.

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Commit messages:
 - Backport e5d3ee394ae940ee0111489e6e072f327ec29c3b

Changes: https://git.openjdk.java.net/jdk16u/pull/120/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16u&pr=120&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266802
  Stats: 76 lines in 3 files changed: 71 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk16u/pull/120.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16u pull/120/head:pull/120

PR: https://git.openjdk.java.net/jdk16u/pull/120