[foreign-memaccess+abi] RFR: 8310893: VarHandleTestExact fails

[Jorn Vernee]

Simple change of `memorySegmentViewVarHandle` -> `varHandle`.

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Commit messages:
 - fix failing test

Changes: https://git.openjdk.org/panama-foreign/pull/842/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=842&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310893
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/842.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign.git pull/842/head:pull/842

PR: https://git.openjdk.org/panama-foreign/pull/842