RFR: 8264827: Large mapped buffer/segment crash the VM when calling isLoaded

[Chris Hegarty]

Avoid overflow when calculating the number of pages for large mapped segment sizes.

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Commit messages:
 - Test update
 - Initial changes

Changes: https://git.openjdk.java.net/jdk/pull/3378/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3378&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264827
  Stats: 32 lines in 5 files changed: 19 ins; 0 del; 13 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3378.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3378/head:pull/3378

PR: https://git.openjdk.java.net/jdk/pull/3378