RFR: 8338675: javac shouldn't silently change .jar files on the classpath

[David Beaumont]

Modifying `JavacFileManager` to skip creating sibling output class files for source files found in JARs.

This should match older (JDK 8) behavior whereby the JAR was not writable, and results in any newly generated class files being written to the current working directory (the output of class files into current directory isn't good, but it should match the old behavior).

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Commit messages:
 - 8338675: javac shouldn't silently change .jar files on the classpath
 - 8338675: javac shouldn't silently change .jar files on the classpath
 - 8338675: javac shouldn't silently change .jar files on the classpath
 - Work in progress.

Changes: https://git.openjdk.org/jdk/pull/23699/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23699&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338675
  Stats: 200 lines in 3 files changed: 196 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/23699.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23699/head:pull/23699

PR: https://git.openjdk.org/jdk/pull/23699