[foreign-memaccess+abi] RFR: Add benchmarks to MemorySegmentVsBits

[Per Minborg]

This PR proposes the addition of some benchmarks, for example using a LonBuffer and a VarHandle.

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Commit messages:
 - Add benchmarks

Changes: https://git.openjdk.org/panama-foreign/pull/762/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=762&range=00
  Stats: 42 lines in 1 file changed: 29 ins; 12 del; 1 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/762.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/762/head:pull/762

PR: https://git.openjdk.org/panama-foreign/pull/762