RFR: 8326957: Implementation of JEP 474: ZGC: Generational Mode by Default [v2]

[Axel Boldt-Christmas]

> This is the implementation task for `JEP 474: ZGC: Generational Mode by Default`. See the JEP for details. [JDK-8326667](https://bugs.openjdk.org/browse/JDK-8326667)

Axel Boldt-Christmas has updated the pull request incrementally with two additional commits since the last revision:

 - Remove extra space
 - Use consistent terminology

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18393/files
  - new: https://git.openjdk.org/jdk/pull/18393/files/ca9492d9..e80424c6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18393&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18393&range=00-01

  Stats: 3 lines in 3 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/18393.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18393/head:pull/18393

PR: https://git.openjdk.org/jdk/pull/18393