RFR: 7260: Create a new serializers bundle [v2]

[Marcus Hirt]

> This creates a new core bundle that can be used to serialize data from JFR into various popular formats, such as DOT and JSON.

Marcus Hirt has updated the pull request incrementally with two additional commits since the last revision:

 - Update core/org.openjdk.jmc.flightrecorder.serializers/src/main/java/org/openjdk/jmc/flightrecorder/serializers/json/FlameGraphJsonSerializer.java
   
   Co-authored-by: Henrik Dafgård <hdafgard at gmail.com>
 - Update core/org.openjdk.jmc.flightrecorder.serializers/src/main/java/org/openjdk/jmc/flightrecorder/serializers/json/FlameGraphJsonSerializer.java
   
   Co-authored-by: Henrik Dafgård <hdafgard at gmail.com>

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Changes:
  - all: https://git.openjdk.java.net/jmc/pull/254/files
  - new: https://git.openjdk.java.net/jmc/pull/254/files/805997bc..fc3fb859

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmc&pr=254&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jmc&pr=254&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jmc/pull/254.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/254/head:pull/254

PR: https://git.openjdk.java.net/jmc/pull/254