RFR: JDK-8317285: Misspellings in hprof test lib

[Alex Menkov]

The change fixes misspelled "referer" in test/lib/jdk/test/lib/hprof library
The only caller of changed public API is VThreadInHeapDump.java

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Commit messages:
 - fix

Changes: https://git.openjdk.org/jdk/pull/16174/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16174&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317285
  Stats: 50 lines in 4 files changed: 0 ins; 0 del; 50 mod
  Patch: https://git.openjdk.org/jdk/pull/16174.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16174/head:pull/16174

PR: https://git.openjdk.org/jdk/pull/16174