RFR: 7124: Support the new JDK 16 allocation profiling event

[Jean-Philippe Bempel]

Add support of ObjectAllocationSample event in HeapPage

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Commit messages:
 - 7124: Support the new JDK 16 allocation profiling event

Changes: https://git.openjdk.java.net/jmc/pull/244/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=244&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-7124
  Stats: 57 lines in 7 files changed: 36 ins; 13 del; 8 mod
  Patch: https://git.openjdk.java.net/jmc/pull/244.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/244/head:pull/244

PR: https://git.openjdk.java.net/jmc/pull/244