RFR: 8361383: LogFileStreamOutput::write_decorations uses wrong type for format precisions

[Kim Barrett]

Please review this change to LogFileStreamOutput to fix the type of the
precision values used when writing the decorations in a log message.

While I was at it, value-initialize the _decorator_padding in the
ctor-initializer rather than with a zero-filling loop.

Testing: mach5 tier1
Locally ran several tests that generate logging output and checked by eye the
decorator output.

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Commit messages:
 - fix precision types in log printing

Changes: https://git.openjdk.org/jdk/pull/26124/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26124&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8361383
  Stats: 9 lines in 2 files changed: 1 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/26124.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26124/head:pull/26124

PR: https://git.openjdk.org/jdk/pull/26124