RFR: 8376023: Reconcile ClassUnloader with ClassUnloadCommon [v2]

[SendaoYan]

> Hi all,
> 
> This PR merge test/hotspot/jtreg/vmTestbase/nsk/share/ClassUnloader.java to test/lib/jdk/test/lib/classloader/ClassUnloadCommon.java, and make the vmTestbase tests use the ClassUnloadCommon.
> 
> The core method in test/hotspot/jtreg/vmTestbase/nsk/share/ClassUnloader.java is `boolean unloadClass()`, and the core method in test/lib/jdk/test/lib/classloader/ClassUnloadCommon.java is `Set<String> triggerUnloading(List<String> classNames)`, it's not easy to combile these two methods to one. So I keep all these two methods.
> 
> Additional testing:
> 
> - [x] Full jtreg tests include vmTestbase

SendaoYan 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 31 additional commits since the last revision:

 - Fix missed attempt++
 - Add "import jdk.test.lib.classloader.CustomClassLoader;" for vmTestbase/nsk/jvmti/scenarios/events/EM01/em01t002/TestDescription.java etc..
 - Adapt DEFAULT_BREAKPOINT_LINE from 63 to 65, since two lines added to test/hotspot/jtreg/vmTestbase/nsk/share/jpda/AbstractDebuggeeTest.java
 - Add "import jdk.test.lib.classloader.ClassFileFinder"
 - fix vmTestbase/nsk/jdi/Scenarios/invokeMethod/redefineclasses001/TestDescription.java fails "cannot find symbol ClassFileFind"
 - sed -i "s|import nsk.share.CustomClassLoader;|import jdk.test.lib.classloader.CustomClassLoader;|" `grep nsk.share.CustomClassLoader test/ -rnl `
 - Fix test/hotspot/jtreg/vmTestbase/nsk/jdi/ClassUnloadEvent/className/classname001/TestDescription.java fails "cannot find user-defined classloader loaded: nsk.share.CustomClassLoader"
 - Fix javac error: "AbstractDebuggeeTest.java:103: error: cannot find symbol"
 - Merge branch 'openjdk:master' into jbs8376023
 - Fix comment in test/hotspot/jtreg/vmTestbase/nsk/jdi/ClassObjectReference/reflectedType/reflectype002/TestDescription.java
 - ... and 21 more: https://git.openjdk.org/jdk/compare/717f7a39...bff25ebf

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/29545/files
  - new: https://git.openjdk.org/jdk/pull/29545/files/458fb127..bff25ebf

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29545&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29545&range=00-01

  Stats: 13921 lines in 367 files changed: 7638 ins; 2803 del; 3480 mod
  Patch: https://git.openjdk.org/jdk/pull/29545.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29545/head:pull/29545

PR: https://git.openjdk.org/jdk/pull/29545