RFR: 8330172: G1: Consolidate update_bot_for_block and update_bot_for_obj in HeapRegion

[Guoxiong Li]

Hi all,

This patch consolidates the methods `update_bot_for_obj` and `update_bot_for_block`. The test `make test-tier1_gc` passed locally.

Thanks for taking the time to review.

Best Regards,
-- Guoxiong

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Commit messages:
 - JDK-8330172

Changes: https://git.openjdk.org/jdk/pull/18771/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18771&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330172
  Stats: 20 lines in 4 files changed: 0 ins; 11 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/18771.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18771/head:pull/18771

PR: https://git.openjdk.org/jdk/pull/18771