RFR: 8294850: Make rs length/pending card predictors dependent on gc type

[Thomas Schatzl]

Hi all,

  can I have reviews for this change that separates `rs_length` and `pending_cards` predictors by young phase?

Some notes:
* this does not intend to improve the predictors themselves - i.e. the use of `xxx_diff` and `xxx` predictors and adding them together is kind of weird, imho trying to add a kind of prediction compensation/improvement to act on differences like a (PID-)controller. I also strongly suspect that the `xxx_diff` predictors ought to be allowed to report negative values. This is no attempt to fix this
* the parameter `for_young_gc` in the analytics API is misnamed. It's not about young gcs, but young_only_phase - I will fix this in a follow-up

Depends on PR#10649, please review that one first.

Thanks, 
  Thomas

Testing: gha, local testing, tier1-5 with other changes in this patch series, perf testing with other changes in this patch series

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Depends on: https://git.openjdk.org/jdk/pull/10649

Commit messages:
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/10650/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10650&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294850
  Stats: 69 lines in 3 files changed: 30 ins; 6 del; 33 mod
  Patch: https://git.openjdk.org/jdk/pull/10650.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10650/head:pull/10650

PR: https://git.openjdk.org/jdk/pull/10650