Running two or more `jlink` invocations concurrently in the same JVM through 
the `ToolProvider` API causes the simultaneous `run` calls to interfere with 
one another, even when each invocation targets a distinct `--output` directory 
and the invocations share no inputs. They may fail with errors such as:

Error: java.lang.IllegalStateException: stream has already been operated upon 
or closed
Error: Resource XYZ already present

The problem is that Main.run(...) correctly creates a new `JlinkTask` for each 
call, but `JlinkTask` defeats this isolation by sharing static `TaskHelper` and 
`OptionsHelper` instances. Concurrent invocations can therefore overwrite one 
another’s parsed options and plugin pipelines.

The proposed solution is to make `taskHelper` and `optionsHelper` instance 
fields of `JlinkTask`. This preserves actual concurrency. Synchronizing the 
provider would unnecessarily serialize image creation and would not protect 
separate provider instances or direct calls to `Main.run(...)`.

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Commit messages:
 - 8390505: jlink is not thread safe when used via ToolProvider API

Changes: https://git.openjdk.org/jdk/pull/32469/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=32469&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8390505
  Stats: 61 lines in 2 files changed: 45 ins; 0 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/32469.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/32469/head:pull/32469

PR: https://git.openjdk.org/jdk/pull/32469

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