RFR: 8351892: GenShen: Remove enforcement of generation sizes [v2]

[William Kemper]

> * The option to configure minimum and maximum sizes for the young generation have been combined into `ShenandoahInitYoungPercentage`.
> * The remaining functionality in `shGenerationSizer` wasn't enough to warrant being its own class, so the functionality was rolled into `shGenerationalHeap`.

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Don't let old have the entire heap

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24268/files
  - new: https://git.openjdk.org/jdk/pull/24268/files/e32ed37c..bc171089

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24268&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24268&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/24268.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24268/head:pull/24268

PR: https://git.openjdk.org/jdk/pull/24268