RFR: 8359825: Parallel: Simplify MutableNUMASpace::ensure_parsability

[Albert Mingkun Yang]

Simple `fill_with_object` -> `fill_with_objects` API  change to push the implementation logic to the callee.

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Commit messages:
 - pgc-fill-words

Changes: https://git.openjdk.org/jdk/pull/25852/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25852&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8359825
  Stats: 12 lines in 1 file changed: 0 ins; 9 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/25852.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25852/head:pull/25852

PR: https://git.openjdk.org/jdk/pull/25852