RFR: 8284532: Memory leak in BitSet::BitMapFragmentTable in JFR leak profiler

[Zhengyu Gu]

BitSet::BitMapFragmentTable needs a destructor to cleanup its contents to avoid leaking hashtable entries and bucket array.

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Commit messages:
 - 8284532: Memory leak in BitSet::BitMapFragmentTable in JFR leak profiler

Changes: https://git.openjdk.java.net/jdk/pull/8148/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8148&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284532
  Stats: 15 lines in 2 files changed: 13 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8148.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8148/head:pull/8148

PR: https://git.openjdk.java.net/jdk/pull/8148