[foreign-memaccess+abi] RFR: 8292174: Add unaligned layouts to ValueLayout [v2]

[Per Minborg]

> The layouts are placed in a special `Unaligned` class. This prevents the classes to be seen on the top level (for less cluttering) and allows lazy initialization of items that are likely not so much used.

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

  Update after PR comments

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Changes:
  - all: https://git.openjdk.org/panama-foreign/pull/705/files
  - new: https://git.openjdk.org/panama-foreign/pull/705/files/968e0f81..a667b610

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-foreign&pr=705&range=01
 - incr: https://webrevs.openjdk.org/?repo=panama-foreign&pr=705&range=00-01

  Stats: 414 lines in 3 files changed: 281 ins; 122 del; 11 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/705.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/705/head:pull/705

PR: https://git.openjdk.org/panama-foreign/pull/705