RFR: 8278856: javac documentation does not mention use of Manifest class-path attribute

[Archie L. Cobbs]

JAR files appearing in `--class-path` are implicitly scanned for manifest `Class-Path` attributes, but this behavior is not documented.

This patch adds a blurb to the `javac(1)` man page.

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Commit messages:
 - Restrict javac command line help output to 80 columns.

Changes: https://git.openjdk.org/jdk/pull/13332/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13332&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8278856
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13332.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13332/head:pull/13332

PR: https://git.openjdk.org/jdk/pull/13332