[foreign-memaccess+abi] RFR: Fix imports

[Per Minborg]

This PR fixes some imports and is related to https://bugs.openjdk.org/browse/JDK-8293510

Two other minor fixes are also included.

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Commit messages:
 - Fix imports

Changes: https://git.openjdk.org/panama-foreign/pull/723/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=723&range=00
  Stats: 60 lines in 11 files changed: 45 ins; 3 del; 12 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/723.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/723/head:pull/723

PR: https://git.openjdk.org/panama-foreign/pull/723