RFR: 8261160: Add a deserialization JFR event

[Chris Hegarty]

This issue adds a new event to improve diagnostic information of Java deserialization. The event captures the details of deserialization activity from ObjectInputStream. The event details are similar to that of the serial filter, but is agnostic of whether a filter is installed or not. The event also captures the filter status, if there is one.

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Commit messages:
 - minor cleanup; all tests passing
 - Unconditionally fire a deser event regardless of filter, and add test
 - commit 2
 - commit 1

Changes: https://git.openjdk.java.net/jdk/pull/2479/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2479&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261160
  Stats: 516 lines in 12 files changed: 496 ins; 5 del; 15 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2479.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2479/head:pull/2479

PR: https://git.openjdk.java.net/jdk/pull/2479