[foreign-jextract] RFR: 8248487: Add static helpers to access segments (continued)

[Maurizio Cimadamore]

Fix jextract tests to use correct memory static accessors.

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Commit messages:
 - Fix jextract tests to use correct static accessors

Changes: https://git.openjdk.java.net/panama-foreign/pull/235/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/235/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8248487
  Stats: 17 lines in 3 files changed: 0 ins; 4 del; 13 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/235.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/235/head:pull/235

PR: https://git.openjdk.java.net/panama-foreign/pull/235