[foreign-jextract] RFR: 8259473: jextract generated code should throw exception for unfound native symbols from calls, variable access, set immediately [v2]

[Athijegannathan Sundararajan]

> NPE with proper error message is thrown immediately (on call, variable access/set)

Athijegannathan Sundararajan has updated the pull request incrementally with one additional commit since the last revision:

  Using UnsatisfiedLinkError and "unresolved symbol: <name>" as error message.
  Refactored static methods in header file class to check linkage outside try
  block around invokeExact - so that UnsatisfiedLinkError, if needed, is thrown.

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Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/432/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/432/files/bc8b043a..c9f5c213

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=432&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=432&range=00-01

  Stats: 41 lines in 4 files changed: 13 ins; 4 del; 24 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/432.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/432/head:pull/432

PR: https://git.openjdk.java.net/panama-foreign/pull/432