RFR: JDK-8300582: Introduce interface for unaligned memory accesses [v3]

[Justin King]

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

Justin King has updated the pull request incrementally with one additional commit since the last revision:

  Simplify byteswap implementation
  
  Signed-off-by: Justin King <jcking at google.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12078/files
  - new: https://git.openjdk.org/jdk/pull/12078/files/b181ce9f..2c4d91eb

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12078&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12078&range=01-02

  Stats: 200 lines in 1 file changed: 114 ins; 46 del; 40 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