RFR: 8320652: ThreadInfo.isInNative needs to be updated to say what executing native code means

[Alan Bateman]

This is a docs only change to j.l.management.ThreadInfo::isInNative. 

The method currently specifies that it tests if the thread is  "executing native code via the Java Native Interface (JNI)".  It would be clearer to say that it tests if the thread is executing a native method, and expand it to include native code invoked using the new foreign linker APIs.

The existing javadoc has wording to try to clarify that "native code" does not include runtime or compiled code. I went through a few iterations to work this in but all attempts just invite more questions and nit picking. To keep it simple, this sentence is dropped so that the method description is focused on the cases where the method returns true.

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Commit messages:
 - Simplify wording
 - Merge
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/16791/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16791&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320652
  Stats: 5 lines in 1 file changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/16791.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16791/head:pull/16791

PR: https://git.openjdk.org/jdk/pull/16791