RFR: JDK-8300582: Introduce interface for unaligned memory accesses

[Justin King]

Introduce interface for unaligned memory accesses `UnalignedAccess`, consolidate the byte swapping implementation to `byteswap`, and switch to a generic implementation of `Bytes`.

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Commit messages:
 - Unaligned access

Changes: https://git.openjdk.org/jdk/pull/12078/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12078&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300582
  Stats: 2246 lines in 25 files changed: 470 ins; 1770 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/12078.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12078/head:pull/12078

PR: https://git.openjdk.org/jdk/pull/12078