[foreign-memaccess+abi] RFR: Fix javadoc "highest-order" rather than "upper"

[Per Minborg]

Minor Javadoc improvements

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Commit messages:
 - Fix javadoc highest-order

Changes: https://git.openjdk.org/panama-foreign/pull/779/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=779&range=00
  Stats: 8 lines in 1 file changed: 0 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/779.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/779/head:pull/779

PR: https://git.openjdk.org/panama-foreign/pull/779