[foreign-memaccess+abi] RFR: Micro optimizations and tidy [v2]

[Per Minborg]

> This small PR adds some optimizations and tidies up some imports.

Per Minborg has updated the pull request incrementally with one additional commit since the last revision:

  Update after comments

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

Changes:
  - all: https://git.openjdk.org/panama-foreign/pull/708/files
  - new: https://git.openjdk.org/panama-foreign/pull/708/files/f93d2249..a3e86044

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-foreign&pr=708&range=01
 - incr: https://webrevs.openjdk.org/?repo=panama-foreign&pr=708&range=00-01

  Stats: 23 lines in 1 file changed: 7 ins; 11 del; 5 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/708.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/708/head:pull/708

PR: https://git.openjdk.org/panama-foreign/pull/708