RFR: 8333229: Parallel: Rename ParMarkBitMap::_region_start to _heap_start

Wed May 29 20:14:23 UTC 2024

Trivial renaming to better capture that this class corresponds to the whole heap mem-region.

-------------

Commit messages:
 - pgc-rename-heap

Changes: https://git.openjdk.org/jdk/pull/19468/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19468&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333229
  Stats: 39 lines in 4 files changed: 0 ins; 13 del; 26 mod
  Patch: https://git.openjdk.org/jdk/pull/19468.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19468/head:pull/19468

PR: https://git.openjdk.org/jdk/pull/19468