[foreign-jextract] RFR: 8258248: jextract should generate jdk 16 compatible code

[Athijegannathan Sundararajan]

using --release 16 option for inmemory java compilation. Using V16 for ASM generated code.

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

Commit messages:
 - 8258248: jextract should generate jdk 16 compatible code

Changes: https://git.openjdk.java.net/panama-foreign/pull/419/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=419&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258248
  Stats: 2 lines in 2 files changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/419.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/419/head:pull/419

PR: https://git.openjdk.java.net/panama-foreign/pull/419