RFR: 8300979: Lazily initialize (byte, char)arr in java.io.DataInputStream

[Per Minborg]

This PR proposed to lazily initialize the scratch arrays only if/when needed.

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Commit messages:
 - Remove redundant initilizers
 - Lazily initialize (byte, char)arr in java.io.DataInputStream

Changes: https://git.openjdk.org/jdk/pull/13121/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13121&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300979
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/13121.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13121/head:pull/13121

PR: https://git.openjdk.org/jdk/pull/13121