RFR: 8286176: Add JNI_VERSION_19 to jni.h and JNI spec

[Alan Bateman]

JNI is updated in Java 19 so we need to define JNI_VERSION_19 and change GetVersion to return this version.

test/hotspot/jtreg/native_sanity/JniVersion.java is updated to check that JNI_VERSION_19 is returned. The native library in the JMX agent, and several tests, define JNI_OnLoad that return JNI_VERSION_10 as the JNI version needed. These are updated to return JNI_VERSION_19 although these updates aren't strictly needed.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk19/pull/7/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk19&pr=7&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8286176
  Stats: 16 lines in 10 files changed: 2 ins; 0 del; 14 mod
  Patch: https://git.openjdk.org/jdk19/pull/7.diff
  Fetch: git fetch https://git.openjdk.org/jdk19 pull/7/head:pull/7

PR: https://git.openjdk.org/jdk19/pull/7