[foreign-memaccess+abi] RFR: 8303888: Add AddressLayout.withoutTargetLayout [v2]

[Per Minborg]

> This PR proposes to add a `AddressLayout.withoutTargetLayout()` method for symmetry reasons. This allows  AddressLayout to be converted back to raw addresses.
> 
> Discussion point: Should this method require native access?

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

  Update after comments

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Changes:
  - all: https://git.openjdk.org/panama-foreign/pull/815/files
  - new: https://git.openjdk.org/panama-foreign/pull/815/files/debafd39..8ed23fe1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-foreign&pr=815&range=01
 - incr: https://webrevs.openjdk.org/?repo=panama-foreign&pr=815&range=00-01

  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/815.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/815/head:pull/815

PR: https://git.openjdk.org/panama-foreign/pull/815