[foreign-memaccess+abi] RFR: Add benchmark [v3]

[Per Minborg]

> This PR proposed to add a new benchmark outlining potential performance gains with the FFM API in internal JDK classes.

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

  Add case for singel invocation

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Changes:
  - all: https://git.openjdk.org/panama-foreign/pull/761/files
  - new: https://git.openjdk.org/panama-foreign/pull/761/files/3b27bcf6..b953b24a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-foreign&pr=761&range=02
 - incr: https://webrevs.openjdk.org/?repo=panama-foreign&pr=761&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/761.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/761/head:pull/761

PR: https://git.openjdk.org/panama-foreign/pull/761