RFR: CODETOOLS-7902928: Improve support for async-profiler 2.x [v4]

[Jason Zaugg]

> Allow multiple events to be captured simultaneously in this version,
> provided that JFR is chosen as output format.
> 
> Delegate output file writing to the async-profiler. This is required
> in 2.x for the JFR output but is supported in both versions. The file
> path must be provided when starting the profiler with JFR output, so
> we need to create the per-trial output directory in the first
> `beforeIteration`.
> 
> Avoid the character '%' in the generated directory name as this
> is interpreted by async-profiler as part %p or %t placeholder.

Jason Zaugg has updated the pull request incrementally with one additional commit since the last revision:

  Further cleanup async-profiler 2.x integration
  
  Co-authored-by: Aleksey Shipilëv <shade at redhat.com>

-------------

Changes:
  - all: https://git.openjdk.java.net/jmh/pull/37/files
  - new: https://git.openjdk.java.net/jmh/pull/37/files/eca51e4b..13e4a0b9

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmh&pr=37&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jmh&pr=37&range=02-03

  Stats: 77 lines in 1 file changed: 16 ins; 24 del; 37 mod
  Patch: https://git.openjdk.java.net/jmh/pull/37.diff
  Fetch: git fetch https://git.openjdk.java.net/jmh pull/37/head:pull/37

PR: https://git.openjdk.java.net/jmh/pull/37