RFR: 8335925: Serial: Move allocation API from Generation to subclasses [v2]

[Albert Mingkun Yang]

> Trivial moving methods from parent class to subclasses. The unused second arg is also removed along the way. The API names are descriptive enough so that the accompanying comments are dropped as well.

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 three additional commits since the last revision:

 - review
 - Merge branch 'master' into s1-gen-alloc
 - s1-gen-alloc

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20084/files
  - new: https://git.openjdk.org/jdk/pull/20084/files/33a7771c..d8d3add6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20084&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20084&range=00-01

  Stats: 4945 lines in 309 files changed: 2462 ins; 1220 del; 1263 mod
  Patch: https://git.openjdk.org/jdk/pull/20084.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20084/head:pull/20084

PR: https://git.openjdk.org/jdk/pull/20084