[foreign-memaccess+abi] RFR: 8292851: MemorySegment arithmetics performed with int accuracy where long is required [v2]

[Per Minborg]

> This PR fixes a potentially severe `int` overflow issue.

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

  Add test and cleanup

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Changes:
  - all: https://git.openjdk.org/panama-foreign/pull/712/files
  - new: https://git.openjdk.org/panama-foreign/pull/712/files/cd4c7a7f..48e82ac2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-foreign&pr=712&range=01
 - incr: https://webrevs.openjdk.org/?repo=panama-foreign&pr=712&range=00-01

  Stats: 61 lines in 2 files changed: 59 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/712.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/712/head:pull/712

PR: https://git.openjdk.org/panama-foreign/pull/712