RFR: 8335925: Serial: Move allocation API from Generation to subclasses [v3]

[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 five additional commits since the last revision:

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

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/20084/files
  - new: https://git.openjdk.org/jdk/pull/20084/files/d8d3add6..cb73df05

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20084&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20084&range=01-02

  Stats: 16460 lines in 487 files changed: 10183 ins; 4373 del; 1904 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