RFR: 8295370: Update java.io.ObjectStreamField to use Class.descriptorString

[Roger Riggs]

The code in ObjectStreamField for constructing type signatures should be replaced by Class.descriptorString(). 
The corresponding change is made in ObjectStreamClass.
There is no change to the contents of the type strings and the existing tests will cover it.

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Commit messages:
 - 8295370: Update java.io.ObjectStreamField to use Class.descriptorString

Changes: https://git.openjdk.org/jdk/pull/10714/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10714&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295370
  Stats: 59 lines in 2 files changed: 0 ins; 53 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/10714.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10714/head:pull/10714

PR: https://git.openjdk.org/jdk/pull/10714