RFR: 8261441: JFR: Filename expansion [v5]

[Denghui Dong]

> Hi,
> Could I have a review of this change that let the users could use `%p` in the filename to represent the PID  when JFR.start/stop/dump.
> 
> I haven't implemented `%t` described in the issue, because I don't think it's very useful.
> 
> Best,
> Denghui Dong

Denghui Dong has updated the pull request incrementally with one additional commit since the last revision:

  null check

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4550/files
  - new: https://git.openjdk.java.net/jdk/pull/4550/files/c69da27b..004270d8

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4550&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4550&range=03-04

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4550.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4550/head:pull/4550

PR: https://git.openjdk.java.net/jdk/pull/4550