RFR: JDK-8316778: test hprof lib: invalid array element type from JavaValueArray.elementSize

[Alex Menkov]

The change fixes 2 issues in hprof test library.
The issue were discovered during test development (logging values of dumped heap objects).
- JavaValueArray.elementSize cannot determine size of the array elements and throws RuntimeException: invalid array element type
- JavaObject.toString() method for dumped String objects tries to construct string value of the object from "value" field assuming "value" field is array of char. Actually it's byte array, so toString return array values like "{65, 66, 67}" (with fixed JavaValueArray.elementSize)

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Commit messages:
 - jcheck
 - hprof lib fix

Changes: https://git.openjdk.org/jdk/pull/15953/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15953&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316778
  Stats: 195 lines in 3 files changed: 184 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/15953.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15953/head:pull/15953

PR: https://git.openjdk.org/jdk/pull/15953