RFR: 8268358: [lworld] toString for primitive class should return `ClassName at hash`

[Mandy Chung]

`Object::toString` implementation of a primitive class should return the traditional `ClassName at hash` (rather than listing the field values) not to leak any private and security-sensitive information.   A primitive class can override `toString` implementation for their custom string representation.

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Commit messages:
 - 8268358: [lworld] toString for primitive class should return `ClassName at hash`

Changes: https://git.openjdk.java.net/valhalla/pull/438/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=438&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268358
  Stats: 193 lines in 24 files changed: 13 ins; 143 del; 37 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/438.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/438/head:pull/438

PR: https://git.openjdk.java.net/valhalla/pull/438