RFR: 8371672: G1: G1YoungGenSizer handling of NewRatio, NewSize and MaxNewSize

[Axel Boldt-Christmas]

G1YoungGenSizer ignores these values if they are not from the command line. Resulting in a different _sizer_kind than expected.
The NewSize and MaxNewSize are also not bounded by the Initial and Max heap size respectively ([JDK-8370494](https://bugs.openjdk.org/browse/JDK-8370494)).

I suggest we rewrite this logic using `!FLAG_IS_DEFAULT` to always get the correct behaviour. And only use `FLAG_IS_CMDLINE` for issuing warnings to the user when we ergonomically change or ignore these values to be compatible.
As well as adding the proper truncation for HeapSize incompatible values.

* Testing
  * GHA
  * Tier 1-5 on Oracle Supported Platforms

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Commit messages:
 - G1: Use of FLAG_IS_CMDLINE for NewRatio, NewSize and MaxNewSize

Changes: https://git.openjdk.org/jdk/pull/28255/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28255&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371672
  Stats: 73 lines in 1 file changed: 49 ins; 1 del; 23 mod
  Patch: https://git.openjdk.org/jdk/pull/28255.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28255/head:pull/28255

PR: https://git.openjdk.org/jdk/pull/28255