RFR: JDK-8234502 : Merge GenCollectedHeap and SerialHeap [v9]

[Lei Zaakjyu]

> JDK-8234502 : Merge GenCollectedHeap and SerialHeap

Lei Zaakjyu has updated the pull request incrementally with one additional commit since the last revision:

  resolve conflicts #1

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16623/files
  - new: https://git.openjdk.org/jdk/pull/16623/files/12c680a3..4a28d0e8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16623&range=08
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16623&range=07-08

  Stats: 145 lines in 7 files changed: 0 ins; 145 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16623.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16623/head:pull/16623

PR: https://git.openjdk.org/jdk/pull/16623