RFR: 8349766: GenShen: Bad progress after degen does not always need full gc

[Kelvin Nilsen]

In generational mode, only upgrade to full GC from degenerated GC if we've done two degenerated cycles in a row and both indicated bad progress.  Otherwise, start another concurrent GC, which will most likely degenerate also.  But this degenerated cycle will reclaim floating garbage within the young generation much more quickly than a full GC would have done.

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Commit messages:
 - Be less eager to upgrade degen to full gc

Changes: https://git.openjdk.org/jdk/pull/23552/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23552&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8349766
  Stats: 20 lines in 2 files changed: 17 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/23552.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23552/head:pull/23552

PR: https://git.openjdk.org/jdk/pull/23552