RFR: 8328602: Parallel: Incorrect assertion in fill_dense_prefix_end [v2]

[Albert Mingkun Yang]

> Relax too-strong assertion about min-filler-size to account for large obj-alignment.
> 
> Test: with explicit large obj-alignment

Albert Mingkun Yang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:

 - review
 - pgc-obj-alignment

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Changes: https://git.openjdk.org/jdk/pull/18396/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18396&range=01
  Stats: 20 lines in 1 file changed: 13 ins; 1 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/18396.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18396/head:pull/18396

PR: https://git.openjdk.org/jdk/pull/18396