RFR: 8345323: Parallel GC does not handle UseLargePages and UseNUMA gracefully

[Albert Mingkun Yang]

This patch reverts the default value of `OldSize` to its previous setting prior to being obsoleted in [JDK-8333962](https://bugs.openjdk.org/browse/JDK-8333962). The change addresses an issue where `OldSize` being set to zero results in a default `MinHeapSize` that is too small to handle LargePages correctly. This problem is exemplified by `ParallelArguments::initialize_heap_flags_and_sizes`, as identified in [JDK-8345323](https://bugs.openjdk.org/browse/JDK-8345323).

Changing the default value of `OldSize` may have broader implications due to the complexity of the logic that determines default values for various flags. Altering one default can lead to cascading effects and potential breakages elsewhere. For these reasons, this patch restores the previous default value of `OldSize` to mitigate such risks.

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Commit messages:
 - pgc-old-size-value

Changes: https://git.openjdk.org/jdk/pull/22575/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22575&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345323
  Stats: 5 lines in 1 file changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/22575.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22575/head:pull/22575

PR: https://git.openjdk.org/jdk/pull/22575