RFR: 8316050: Use hexadecimal encoding in MemorySegment::toString

[Per Minborg]

This PR proposes to use hexadecimal representation for a memory segment address rather than a decimal one.

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Commit messages:
 - Use hexadecimal encoding in MemorySegment::toString

Changes: https://git.openjdk.org/jdk/pull/15670/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15670&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316050
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15670.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15670/head:pull/15670

PR: https://git.openjdk.org/jdk/pull/15670