RFR: 8276548: Use range based visitor for Howl-Full cards

[Thomas Schatzl]

Hi all,

  can I have reviews for this change that improves the way G1 iterates over Howl-Full containers (i.e. "Full" cardsetptrs within a Howl cardset container)? Instead of calling the visitor method `do_card` to mark a single card for all cards in the range, just call the range-based visitor method `do_card_range`. This is also a little bit more efficient.

This change is a requirement for [JDK-8275056](https://bugs.openjdk.java.net/browse/JDK-8275056).

Testing: tier1-5

Thanks,
  Thomas

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Commit messages:
 - Merge branch '8276540-howl-full-bitmap' into 8276548-range-based-visitor
 - Fix
 - Remove debug code
 - Fix length of entry

Changes: https://git.openjdk.java.net/jdk/pull/6230/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6230&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276548
  Stats: 14 lines in 2 files changed: 2 ins; 5 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6230.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6230/head:pull/6230

PR: https://git.openjdk.java.net/jdk/pull/6230