blindspot on `RemoveUnusedImportsStep`

Start at RemoveUnusedImportsStep and trace how unused static imports are detected, using the ExportUtil example as the reproduction. Done means Spotless detects and removes the unused static import without affecting imports that are still referenced.

Only PMD found the unused stuff, spot missed:

• https://github.com/quarkusio/quarkus/pull/48414
• https://github.com/diffplug/spotless/pull/2531

[WARNING] PMD Failure: io.quarkus.test.ExportUtil:3 Rule:UnnecessaryImport Priority:4 Unused static import 'io.quarkus.test.ExportUtil.APPLICATION_PROPERTIES'.

package io.quarkus.test;

import static io.quarkus.test.ExportUtil.APPLICATION_PROPERTIES;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.StringReader;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Comparator;
import java.util.Properties;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import org.jboss.shrinkwrap.api.Node;
import org.jboss.shrinkwrap.api.asset.Asset;
import org.jboss.shrinkwrap.api.asset.StringAsset;
import org.jboss.shrinkwrap.api.exporter.ZipExporter;
import org.jboss.shrinkwrap.api.spec.JavaArchive;

final class ExportUtil {

    static final String APPLICATION_PROPERTIES = "application.properties";

    private ExportUtil() {
    }

    static void exportToQuarkusDeploymentPath(JavaArchive archive) throws IOException {
        String exportPath = System.getProperty("quarkus.deploymentExportPath");
        if (exportPath == null) {
            return;
        }
        File exportDir = new File(exportPath);
        if (exportDir.exists()) {
            if (!exportDir.isDirectory()) {
                throw new IllegalStateException("Export path is not a directory: " + exportPath);
            }
            try (Stream<Path> stream = Files.walk(exportDir.toPath())) {
                stream.sorted(Comparator.reverseOrder()).map(Path::toFile)
                        .forEach(File::delete);
            }
        } else if (!exportDir.mkdirs()) {
            throw new IllegalStateException("Export path could not be created: " + exportPath);
        }
        File exportFile = new File(exportDir, archive.getName());
        archive.as(ZipExporter.class).exportTo(exportFile);
    }

    static void mergeCustomApplicationProperties(JavaArchive archive, Properties customApplicationProperties)
            throws IOException {
        Node applicationProperties = archive.get(APPLICATION_PROPERTIES);
        if (applicationProperties != null) {
            // Merge the existing "application.properties" asset and overriden config properties
            // Overriden properties take precedence
            Properties mergedProperties = new Properties();
            Asset asset = applicationProperties.getAsset();
            if (asset instanceof StringAsset strAsset) {
                mergedProperties.load(new StringReader(strAsset.getSource()));
            } else {
                try (InputStream in = asset.openStream()) {
                    mergedProperties.load(in);
                }
            }
            customApplicationProperties.forEach(mergedProperties::put);

            if (Boolean.parseBoolean(System.getProperty("quarkus.test.log-merged-properties"))) {
                System.out.println("Merged config properties:\n"
                        + mergedProperties.keySet().stream().map(Object::toString).collect(Collectors.joining("\n")));
            } else {
                System.out.println(
                        "NOTE: overrideConfigKey() and application.properties were merged; use quarkus.test.log-merged-properties=true to list the specific values");
            }
            deleteApplicationProperties(archive);
            archive.add(new PropertiesAsset(mergedProperties), APPLICATION_PROPERTIES);
        } else {
            archive.add(new PropertiesAsset(customApplicationProperties), APPLICATION_PROPERTIES);
        }
    }

    static void deleteApplicationProperties(JavaArchive archive) {
        // MemoryMapArchiveBase#addAsset(ArchivePath,Asset) does not overwrite the existing node correctly
        // https://github.com/shrinkwrap/shrinkwrap/issues/179
        archive.delete(APPLICATION_PROPERTIES);
    }
}