RFR: 8321216: SerialGC attempts to access the card table beyond the end of the heap during card table scan

[Thomas Schatzl]

Hi all,

  please review this fix to ` CardTableRS::find_first_clean_card` where when iterating through the object at the very end of the heap Serial GC accesses the card table beyond the allocated memory, which fails with an assert.

The fix is to allow retrieving addresses for cards beyond the card table using a special `addr_for_raw` method. 

In discussions with @albertnetymk , the initial version to add a check whether the current scan cursor is already at or beyond the end of the area to find clean cards for using an extra, somewhat superfluous parameter has been rejected as a bit confusing (the first commit).

Testing: failing test case, gha

Thanks,
  Thomas

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Commit messages:
 - visibility of addr_for_raw
 - whitespace fix
 - discussion-with-ayang-use-addr_for_raw-instead-of-extra parameter
 - initial version

Changes: https://git.openjdk.org/jdk/pull/16968/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16968&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321216
  Stats: 25 lines in 2 files changed: 19 ins; 3 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/16968.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16968/head:pull/16968

PR: https://git.openjdk.org/jdk/pull/16968