RFR: 8359472: JVM crashes when attaching a dynamic agent before JVMTI_PHASE_LIVE [v14]

[Francesco Andreuzzi]

> In this PR I add a check to prevent debug builds to crash when an agent tries to attach while the JVM is not in live phase.
> 
> Passes tier1 and tier2 (fastdebug).

Francesco Andreuzzi has updated the pull request incrementally with five additional commits since the last revision:

 - jvmti errors
 - indent
 - close
 - rephrase
 - PidJcmdExecutor. unused import. cc

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27766/files
  - new: https://git.openjdk.org/jdk/pull/27766/files/30b2cf96..925f9fc8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27766&range=13
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27766&range=12-13

  Stats: 59 lines in 2 files changed: 19 ins; 14 del; 26 mod
  Patch: https://git.openjdk.org/jdk/pull/27766.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27766/head:pull/27766

PR: https://git.openjdk.org/jdk/pull/27766