RFR: 8287024: G1: Improve the API boundary between HeapRegionRemSet and G1CardSet

[Thomas Schatzl]

Hi all,

  can I get reviews for this small refactoring that clarifies the boundaries of what kind of data `HeapRegionRemSet` and `G1CardSet` should operate on?

* `HeapRegionRemSet` deals with addresses, heap regions
* `G1CardSet` deals with card indexes in the heap, card regions and cards within card regions

The `G1CardSet::add_card()` and `G1CardSet::contains_card()` methods are fuzzy about that, they require the caller (`HeapRegionRemSet`) to know about card regions and cards within regions. 

Testing: gha

Thanks,
  Thomas

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Commit messages:
 - initial version

Changes: https://git.openjdk.java.net/jdk/pull/8790/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8790&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287024
  Stats: 146 lines in 5 files changed: 81 ins; 54 del; 11 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8790.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8790/head:pull/8790

PR: https://git.openjdk.java.net/jdk/pull/8790