RFR: 8254234 - Add test library stream object builder

[Chris Hegarty]

It is useful to have a test library facility for building stream objects, suitable for deserialization testing. We
already have a partial implementation in one of the record serialization tests, move it to the test library for more
general use. The implementation remains partial, but can be expanded as and when needed.

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Commit messages:
 - Initial changes for 8254234 - Add test library stream object builder

Changes: https://git.openjdk.java.net/jdk/pull/561/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=561&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254234
  Stats: 409 lines in 2 files changed: 220 ins; 169 del; 20 mod
  Patch: https://git.openjdk.java.net/jdk/pull/561.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/561/head:pull/561

PR: https://git.openjdk.java.net/jdk/pull/561