[foreign-memaccess+abi] RFR: Simplify code now that bitSize is always aligned to byte boundaries

[Per Minborg]

This PR suggests some simplifications now that layouts are always aligned to byte boundaries. 

The PR also contains some other simplifications/cleanups.

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Commit messages:
 - Add copyright years and clean up
 - Simplify code for bit/byte alignment

Changes: https://git.openjdk.org/panama-foreign/pull/796/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=796&range=00
  Stats: 64 lines in 7 files changed: 9 ins; 20 del; 35 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/796.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/796/head:pull/796

PR: https://git.openjdk.org/panama-foreign/pull/796