RFR: 8357976: GenShen crash in swap_card_tables: Should be clean

[William Kemper]

Degenerated cycles must also clean the `read` card table before swapping it with the `write` card table.

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Commit messages:
 - Merge remote-tracking branch 'jdk/master' into clean-read-table-for-degen
 - Clean the read table before swapping during a degenerated cycle

Changes: https://git.openjdk.org/jdk/pull/25735/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25735&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357976
  Stats: 17 lines in 2 files changed: 10 ins; 4 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/25735.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25735/head:pull/25735

PR: https://git.openjdk.org/jdk/pull/25735