RFR: JDK-8269202: Support %p in jfr dump file name

[Hamlin Li]

Currently, jfr supports 2 ways to name dump file.
1. dump without a file name, it will generate a name automatically with pid.
2. specify a file name explicitly, but without support for pid(%p)
It will be helpful to support %p in file name.

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Commit messages:
 - add <pid> for jfr dump file

Changes: https://git.openjdk.java.net/jdk/pull/4564/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4564&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8269202
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4564.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4564/head:pull/4564

PR: https://git.openjdk.java.net/jdk/pull/4564