Fix deleteQuietly handling for symlinked directories

[Sn0wyDay]

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Summary

This PR updates FileUtils.deleteQuietly(File) so that it does not clean the target contents when the input is a symbolic link to a directory.

Previously, deleteQuietly() checked file.isDirectory() and then called cleanDirectory(file) before deleting the file. On platforms where a symbolic link to a directory is treated as a directory, this could remove the contents of the symlink target before deleting the symlink itself.

deleteDirectory() already avoids this behavior by checking !isSymlink(directory) before cleaning directory contents. This PR applies the same safety check to deleteQuietly() for consistency.

Change

Before:

if (file.isDirectory()) {
    cleanDirectory(file);
}

After:

if (file.isDirectory() && !isSymlink(file)) {
    cleanDirectory(file);
}

Tests

Added a regression test that verifies all of the following:

• the symbolic-link directory entry itself is removed;
• the target directory still exists;
• the file inside the target directory is preserved.

The link assertion uses Files.exists(path, LinkOption.NOFOLLOW_LINKS) so it checks the link entry rather than following the link to its target.

Validation completed with Eclipse Temurin JDK 25:

mvn -Dtest=FileUtilsCleanSymlinksTest test
mvn

The default Maven build passed with 6,616 tests run, 0 failures, and 0 errors. Checkstyle, SpotBugs, PMD, license, coverage, and Javadoc checks also passed.

AI tooling disclosure

An OpenAI coding assistant helped identify the candidate, refine the regression-test assertion, investigate the CI failure, and draft the initial explanation. The final code and tests were manually reviewed and validated with the commands listed above.

[Sn0wyDay]

This PR is ready for review. The remaining GitHub Actions workflows are awaiting maintainer approval; could a maintainer please approve them when convenient? Thank you.

[garydgregory]

This is in my queue, I should be able to get to it this week.