[foreign-memaccess+abi] RFR: 8303666: Move address layout outside of ValueLayout namespace [v3]

[Maurizio Cimadamore]

> This patch moves ValueLayout.OfAddress into a toplevel class. This seems desirable since address layouts are very important in the FFM API, and also provides seadditional methods on top of `ValueLayout` to get/set a *target layout*.

Maurizio Cimadamore has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:

 - Simplify AddressLayout javadoc
 - Merge branch 'foreign-memaccess+abi' into address_layout_move
 - Add copyright header
 - Initial push

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Changes: https://git.openjdk.org/panama-foreign/pull/811/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=811&range=02
  Stats: 268 lines in 31 files changed: 133 ins; 72 del; 63 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/811.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/811/head:pull/811

PR: https://git.openjdk.org/panama-foreign/pull/811