[foreign-memaccess+abi] RFR: 8303879: Add MemoryLayout.withNoName()

[Per Minborg]

This PR proposes to add a method `MemoryLayout::withNoName` which allows `MemoryLayout` instances to be checked for functional equivalence (i.e. "everything except the name is the same"). This might be useful for reuse, caching etc. of MemoryLayouts and constructs that consists/depends on one or more `MemoryLayout` instance.

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Commit messages:
 - Cleanup test
 - Add MemoryLayout.withNoName()

Changes: https://git.openjdk.org/panama-foreign/pull/814/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=814&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303879
  Stats: 150 lines in 10 files changed: 131 ins; 0 del; 19 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/814.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/814/head:pull/814

PR: https://git.openjdk.org/panama-foreign/pull/814