Aggregate maven.project.dependencies fileset omits artifacts not in the local repository (reactor builds)

## Summary
The aggregate `maven.project.dependencies` fileset produced by `DependencyFilesetsTask` is rooted at the local repository and uses `localRepository.pathOf(artifact)` for its includes. Artifacts that are not physically located in the local repository (notably reactor inter-module dependencies, resolved to a sibling module's `target/` directory) silently match nothing, so the aggregate fileset is incomplete in reactor builds.

## Affected code
`src/main/java/org/apache/maven/ant/tasks/DependencyFilesetsTask.java` lines 63-85 (master @ `441382c`)

```java
FileSet dependenciesFileSet = new FileSet();
dependenciesFileSet.setProject(getProject());
ArtifactRepository localRepository = getProject().getReference("maven.local.repository");
dependenciesFileSet.setDir(new File(localRepository.getBasedir()));
...
for (Artifact artifact : depArtifacts) {
String relativeArtifactPath = localRepository.pathOf(artifact);
dependenciesFileSet.createInclude().setName(relativeArtifactPath);
...
FileSet singleArtifactFileSet = new FileSet();
singleArtifactFileSet.setProject(getProject());
singleArtifactFileSet.setFile(artifact.getFile());
getProject().addReference(fileSetName, singleArtifactFileSet);
}
```

## Problem
The per-dependency filesets correctly point at `artifact.getFile()` (the actual resolved location), but the aggregate fileset is based on the local repository directory plus the *would-be* installed path from `localRepository.pathOf(artifact)`. In a reactor build, a dependency on a sibling module resolves to that module's output directory (e.g. `module/target/classes` or the built jar), which is **not** present under the local repository — so the aggregate fileset silently omits those dependencies. The same applies to any artifact resolved from a non-default location. Users consuming `maven.project.dependencies` in reactor builds get an incomplete (or empty) fileset with no warning.

## Expected behavior
The aggregate fileset should be assembled from the actual resolved artifact files (as the per-dependency filesets are), rather than from paths reconstructed against the local repository.