[jdk11u-dev] RFR: 8275051: Shenandoah: Correct ordering of requested gc cause and gc request flag

[Zhengyu Gu]

I would like to backport this Shenandoah specific patch to 11u.

The patch corrects the order of a couple of GC flags, ensure GC sees latest GC cause when a GC is requested.

The original patch does not apply cleanly, due to context differences, especially, the grand refactoring in 17. The conflicts are resolved manually.

Test:
- [x] hotspot_gc_shenandoah

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Commit messages:
 - Fix merge error

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/533/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=533&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275051
  Stats: 12 lines in 1 file changed: 6 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/533.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/533/head:pull/533

PR: https://git.openjdk.java.net/jdk11u-dev/pull/533