RFR: 8319932: [JVMCI] class unloading related tests can fail on libgraal [v3]

[Doug Simon]

> This PR addresses a race in `runtime/ClassInitErrors/InitExceptionUnloadTest.java` that is exposed by libgraal which sets the [default value for `TypeProfileWidth` to 8](https://github.com/openjdk/jdk/blob/eb4b6fa6212380c9b6d3c94f5aa3384f12a0c125/src/hotspot/share/compiler/compilerDefinitions.cpp#L429).
> 
> The problem is that `InitExceptionUnloadTest$SpecialException` is loaded by a [custom class loader](https://github.com/openjdk/jdk/blob/eb4b6fa6212380c9b6d3c94f5aa3384f12a0c125/test/hotspot/jtreg/runtime/ClassInitErrors/InitExceptionUnloadTest.java#L106) and appears in the profile of `String.valueOf` as shown by `-XX:+PrintMethodData`:
> 
> static java.lang.String::valueOf(Ljava/lang/Object;)Ljava/lang/String;
>   interpreter_invocation_count: 957
>   invocation_counter: 957
>   backedge_counter: 0
>   decompile_count: 0
>   mdo size: 496 bytes
> 
>    0 nofast_aload_0
>    1 ifnonnull 10
>   0 bci: 1 BranchData taken(698) displacement(56)
>                                     not taken(0)
>    4 fast_aldc_w "null"
>    7 goto 14
>   32 bci: 7 JumpData taken(0) displacement(168)
>   10 nofast_aload_0
>   11 invokevirtual 1023 <java/lang/Object.toString()Ljava/lang/String;>
>   56 bci: 11 VirtualCallData count(2) entries(8)
>                                     'java/lang/String'(470 0.67)
>                                     'java/lang/StackTraceElement'(204 0.29)
>                                     'java/lang/Error'(1 0.00)
>                                     'java/lang/NoClassDefFoundError'(6 0.01)
>                                     'java/lang/ExceptionInInitializerError'(8 0.01)
>                                     'InitExceptionUnloadTest$SpecialException'(2 0.00)          <===== unloadable type in profile
>                                     'java/lang/OutOfMemoryError'(2 0.00)
> 
> 
> When this method is being compiled at tier 3, C1 makes a strong GC root for each type in the profile. Only once the compilation completes, are these strong roots released.
> 
> The test currently triggers class unloading via a [whitebox full GC](https://github.com/openjdk/jdk/blob/eb4b6fa6212380c9b6d3c94f5aa3384f12a0c125/test/lib/jdk/test/lib/classloader/ClassUnloadCommon.java#L67) and then immediately expects the classes to be unloaded. If the above C1 compilation is still in progress, the classes may not yet be unloaded.
> 
> This PR modifies the test to add a retry loop around the unloading trigger and the check for unloaded classes.

Doug Simon 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 four additional commits since the last revision:

 - Merge remote-tracking branch 'openjdk-jdk/master' into JDK-8319932_v2
 - improved javadoc as requested
 - move retry loop for class unloading to lib code
 - allow more time for class unloading in InitExceptionUnloadTest

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/18044/files
  - new: https://git.openjdk.org/jdk/pull/18044/files/3ebec867..e231f627

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18044&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18044&range=01-02

  Stats: 74492 lines in 1542 files changed: 3371 ins; 68046 del; 3075 mod
  Patch: https://git.openjdk.org/jdk/pull/18044.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18044/head:pull/18044

PR: https://git.openjdk.org/jdk/pull/18044