[foreign-memaccess+abi] RFR: Add stack walk test case that doesn't verify oops

[Jorn Vernee]

This is a followup for the earlier quickfix of: https://github.com/openjdk/panama-foreign/pull/417

This adds another test case to TestStackWalk that catches the failing code path.

This re-uses the previously added `WhiteBox::verifyFrames`, and adds a flag to turn off the verification, which triggers the problematic code path. (I've also renamed this to just `walkFrames`, since now we don't always do verification anymore.

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Commit messages:
 - Add stack walk test case that doesn't verify oops

Changes: https://git.openjdk.java.net/panama-foreign/pull/423/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=423&range=00
  Stats: 11 lines in 3 files changed: 3 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/423.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/423/head:pull/423

PR: https://git.openjdk.java.net/panama-foreign/pull/423