[foreign-jextract] Integrated: 8249803: Add LibraryLookup.Symbol

[Maurizio Cimadamore]

This patch fixes jextract's RuntimeHelper to use LibraryLookup.Symbol instead of MemoryAddress, which is causing some
build and test issues.

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Commit messages:
 - Fixup RuntimeHelper to use LibraryLookup.Symbol

Changes: https://git.openjdk.java.net/panama-foreign/pull/258/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/258/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8249803
  Stats: 8 lines in 2 files changed: 1 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/258.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/258/head:pull/258

PR: https://git.openjdk.java.net/panama-foreign/pull/258