RFR: 8371825: G1: Ues more precise filler API in fill_range_with_dead_objects

[Albert Mingkun Yang]

Replace `fill_with_objects` with `fill_with_object` for dead-space inside a heap-region.

Test: tier1-5

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Commit messages:
 - g1-zap

Changes: https://git.openjdk.org/jdk/pull/28302/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28302&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371825
  Stats: 15 lines in 1 file changed: 0 ins; 10 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/28302.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28302/head:pull/28302

PR: https://git.openjdk.org/jdk/pull/28302