Reduce churn when parsing Jar files

Update CentralDirectoryParser to reduce the number of objects created
when parsing the central directory. A single CentralDirectoryFileHeader
object is now reused as entries are parsed.

Fixes gh-5260

spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/jar/CentralDirectoryParserTests.java

@@ -105,7 +105,7 @@ public class CentralDirectoryParserTests {
 		@Override
 		public void visitFileHeader(CentralDirectoryFileHeader fileHeader,
 				int dataOffset) {
-			this.headers.add(fileHeader);
+			this.headers.add(fileHeader.clone());
 		}
 
 		@Override