RFR: 8278568: Consolidate filler objects

Wed Dec 15 20:46:24 UTC 2021

In PSPromotionLAB exists some code that fills unused tails of promotion LABs, which is semantically the same as the CollectedHeap::fill* family of methods. They can be consolidated.

We also have ContiguousSpace::allocate_temporary_filler() which does the same, but is unused and can be removed. 

Testing:
 - [x] hotspot_gc
 - [x] tier1
 - [ ] tier2
 - [ ] tier3

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Commit messages:
 - 8278568: Consolidate filler objects

Changes: https://git.openjdk.java.net/jdk/pull/6814/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6814&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278568
  Stats: 63 lines in 6 files changed: 1 ins; 56 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6814.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6814/head:pull/6814

PR: https://git.openjdk.java.net/jdk/pull/6814