Micro-optimizations to Plugin data to reduce minimum memory for Jenkins (#3654)

* Reduce memory footprint for the plugin info by presizing hashmaps to reduce waste for small maps and interning commonly duplicated plugin strings

* Replace duplicated empty string arrays with the one in MemoryReductionUtil

* Fix interning where strings are null

* Fix to deal with the fact that we directly mutate dependency fields for UpdateSite, sigh

* Reduce starting HashMap size for some hashmaps likely to be empty or tiny

* Cleanup per review comments

* Trim some extra waste out of the UpdateSite warnings

* Fix count of optional dependencies

* Move predicates for dependency matching to top-level static final field so they are not duplicated

core/src/main/java/hudson/Util.java

@@ -26,6 +26,7 @@ package hudson;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 
 import hudson.model.TaskListener;
+import jenkins.util.MemoryReductionUtil;
 import hudson.util.QuotedStringTokenizer;
 import hudson.util.VariableResolver;
 import jenkins.util.SystemProperties;
@@ -92,7 +93,6 @@ import javax.annotation.Nullable;
 import javax.crypto.SecretKey;
 import javax.crypto.spec.SecretKeySpec;
 
-import org.apache.commons.codec.digest.DigestUtils;
 import org.apache.commons.io.FileUtils;
 
 /**
@@ -1388,7 +1388,7 @@ public class Util {
             @Nonnull String symlinkPath, @Nonnull TaskListener listener) throws InterruptedException {
         try {
             Path path = fileToPath(new File(baseDir, symlinkPath));
-            Path target = Paths.get(targetPath, new String[0]);
+            Path target = Paths.get(targetPath, MemoryReductionUtil.EMPTY_STRING_ARRAY);
 
             final int maxNumberOfTries = 4;
             final int timeInMillis = 100;