Open loader jar URLs by default using `runtimeVersion`

Update `UrlJarFileFactory` so that `runtimeVersion` is used by default
instead of `baseVersion`. Prior to this commit we tried to mirror the
JDK handler on look for a `#runtime` fragment. This unfortunately
doesn't work with the URLs produced by `URLClassPath`.

This commit also fixes a bug in `NestedJarFile` where we didn't return
the correct result from `hasEntry`.

Fixes gh-38050

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/NestedJarFile.java

@@ -230,7 +230,7 @@ public class NestedJarFile extends JarFile {
 		}
 		ZipContent.Entry entry = getVersionedContentEntry(name);
 		if (entry != null) {
-			return false;
+			return true;
 		}
 		synchronized (this) {
 			ensureOpen();

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/net/protocol/jar/UrlJarFileFactory.java

@@ -58,7 +58,12 @@ class UrlJarFileFactory {
 	}
 
 	private Runtime.Version getVersion(URL url) {
-		return "runtime".equals(url.getRef()) ? JarFile.runtimeVersion() : JarFile.baseVersion();
+		// The standard JDK handler uses #runtime to indicate that the runtime version
+		// should be used. This unfortunately doesn't work for us as
+		// jdk.internal.loaderURLClassPath only adds the runtime fragment when the URL
+		// is using the internal JDK handler. We need to flip the default to use
+		// the runtime version. See gh-38050
+		return "base".equals(url.getRef()) ? JarFile.baseVersion() : JarFile.runtimeVersion();
 	}
 
 	private boolean isLocalFileUrl(URL url) {