[foreign-memaccess+abi] RFR: Fix the use of final and static

[Per Minborg]

This PR proposes to clean up some of the usages of the `final` and `static` keyword.

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Commit messages:
 - Fix the use of final

Changes: https://git.openjdk.org/panama-foreign/pull/889/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=889&range=00
  Stats: 9 lines in 4 files changed: 0 ins; 2 del; 7 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/889.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign.git pull/889/head:pull/889

PR: https://git.openjdk.org/panama-foreign/pull/889