[foreign-memaccess+abi] RFR: Fix Sonar warnings in jdk.internal.foreign [v2]

[Per Minborg]

> This PR proposes to do some minor fixes and cleanups for warnings that were flagged by Sonar.

Per Minborg has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Reintroduce import
 - Merge branch 'foreign-memaccess+abi' into sonar-internal-foreign
 - Fix Sonar warnings in jdk.internal.foreign

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

Changes:
  - all: https://git.openjdk.org/panama-foreign/pull/905/files
  - new: https://git.openjdk.org/panama-foreign/pull/905/files/02a83006..6fe6dc03

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-foreign&pr=905&range=01
 - incr: https://webrevs.openjdk.org/?repo=panama-foreign&pr=905&range=00-01

  Stats: 24411 lines in 835 files changed: 15419 ins; 5322 del; 3670 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/905.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign.git pull/905/head:pull/905

PR: https://git.openjdk.org/panama-foreign/pull/905