RFR: 8310311: Serial: move Generation::contribute_scratch to DefNewGeneration [v2]

[Albert Mingkun Yang]

> Simple cleanup to move a method from base-class to  sub-class.
> 
> Test: hotspot_gc

Albert Mingkun Yang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains one additional commit since the last revision:

  s1-contribute-scratch

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/14540/files
  - new: https://git.openjdk.org/jdk/pull/14540/files/443fa29e..91970dc9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14540&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14540&range=00-01

  Stats: 22983 lines in 994 files changed: 10908 ins; 5800 del; 6275 mod
  Patch: https://git.openjdk.org/jdk/pull/14540.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14540/head:pull/14540

PR: https://git.openjdk.org/jdk/pull/14540