RFR: 8165276: Spec states to invoke the premain method in an agent class if it's public but implementation differs [v12]

[Serguei Spitsyn]

> This change have been already reviewed by Mandy, Sundar, Alan and David.
> Please, see the jdk 15 review thread:
>   http://mail.openjdk.java.net/pipermail/serviceability-dev/2020-June/031998.html
> 
> Now, the PR approval is needed.
> The push was postponed because the CSR was not approved at that time (it is now):
>    https://bugs.openjdk.java.net/browse/JDK-8248189
> Investigation of existing popular java agents was requested by Joe.
> ----------
> 
> The java.lang.instrument spec:
>   https://docs.oracle.com/en/java/javase/15/docs/api/java.instrument/java/lang/instrument/package-summary.html
> 
> Summary:
>   The java.lang.instrument spec clearly states:
>     "The agent class must implement a public static premain method
>      similar in principle to the main application entry point."
>   Current implementation of sun/instrument/InstrumentationImpl.java
>   allows the premain method be non-public which violates the spec.
>   This fix aligns the implementation with the spec.
> 
> Testing:
>   A mach5 run of jdk_instrument tests is in progress.

Serguei Spitsyn has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 12 additional commits since the last revision:

 - Merge
 - 1. Prperly reverted fixes in 3 tests; 2. Got rid of <inherited> term in tests summary comment
 - @summary of some negative tests is corrected
 - 1. Suppress premain method check only if agent class is in unnamed module; 2. minor tests cleanup
 - added to NegativeAgentRunner exit value check to be non-zero
 - 1. Replaced AgentJarBuilder with JavaAgentBuilder; 2. Removed unneeded sun.tools.jar imports
 - fixed trailing spaces
 - (1) Update premain/agentmain method lookup; (2) refactored tests to get rid of shell scripts
 - added 8165276 to @bug list of impacted tests
 - (1)Fix comment in InstrumentationImpl; (2) Update agent super classes in tests with new expectations that premain methods in supers should non be called
 - ... and 2 more: https://git.openjdk.java.net/jdk/compare/06cc1b7a...d926e4b1

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1694/files
  - new: https://git.openjdk.java.net/jdk/pull/1694/files/219a2cd6..d926e4b1

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1694&range=11
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1694&range=10-11

  Stats: 114388 lines in 3016 files changed: 55977 ins; 36917 del; 21494 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1694.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1694/head:pull/1694

PR: https://git.openjdk.java.net/jdk/pull/1694