RFR: CODETOOLS-7903486: JMH: Revisit available jmh.executor options

[Aleksey Shipilev]

We currently have a few executor options in JMH. As [CODETOOLS-7903476](https://bugs.openjdk.org/browse/CODETOOLS-7903476) shows, not all of them are ready to be used.

GitHub hits:
 "jmh.executor=CACHED_TPE", 0 hits
 "jmh.executor=FIXED_TPE", 0 hits
 "jmh.executor=VIRTUAL_TPE", 0 hits
 "jmh.executor=FJP", 3 hits (various forks of jsoniter)
 "jmh.executor=FJP_COMMON", 0 hits
 "jmh.executor=CUSTOM", 99 hits (various projects)

Looks like CACHED_TPE and FJP_COMMON can go away.
Others are renamed to capture their major characteristic.

Some light bikeshedding about the names is welcome.

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Commit messages:
 - Work

Changes: https://git.openjdk.org/jmh/pull/108/files
 Webrev: https://webrevs.openjdk.org/?repo=jmh&pr=108&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903486
  Stats: 41 lines in 1 file changed: 0 ins; 34 del; 7 mod
  Patch: https://git.openjdk.org/jmh/pull/108.diff
  Fetch: git fetch https://git.openjdk.org/jmh.git pull/108/head:pull/108

PR: https://git.openjdk.org/jmh/pull/108