Rewrite nested jar support code and remove Java 8 support

Rewrite nested jar code to better align with the implementations
provided in Java 17. This update makes two fundamental changes to
the previous implementation:

- Resource cleanup is now handled using the `java.lang.ref.Cleaner`

- Jar URLs now use the form `jar:nested:/my.jar/!nested.jar!/entry`

Unlike the previous `jar🫙/my,jar!/nested.jar!/entry` URL format,
the new format is compatible with Java's default Jar URL handler.
Specifically, it now only uses a single `jar:` prefix and it no longer
includes multiple `!/` separators.

In addition to the changes above, many of the ancillary classes have
also been refactored and updated to create cleaner APIs.

Closes gh-37668

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/tasks/bundling/AbstractBootArchiveTests.java

@@ -256,7 +256,8 @@ abstract class AbstractBootArchiveTests<T extends Jar & BootArchive> {
 		this.task.getMainClass().set("com.example.Main");
 		executeTask();
 		try (JarFile jarFile = new JarFile(this.task.getArchiveFile().get().getAsFile())) {
-			assertThat(jarFile.getEntry("org/springframework/boot/loader/LaunchedURLClassLoader.class")).isNotNull();
+			assertThat(jarFile.getEntry("org/springframework/boot/loader/launch/LaunchedClassLoader.class"))
+				.isNotNull();
 			assertThat(jarFile.getEntry("org/springframework/boot/loader/")).isNotNull();
 		}
 		// gh-16698
@@ -275,7 +276,8 @@ abstract class AbstractBootArchiveTests<T extends Jar & BootArchive> {
 			.getAttributes()
 			.put("Main-Class", "org.springframework.boot.loader.launch.PropertiesLauncher");
 		try (JarFile jarFile = new JarFile(this.task.getArchiveFile().get().getAsFile())) {
-			assertThat(jarFile.getEntry("org/springframework/boot/loader/LaunchedURLClassLoader.class")).isNotNull();
+			assertThat(jarFile.getEntry("org/springframework/boot/loader/launch/LaunchedClassLoader.class"))
+				.isNotNull();
 			assertThat(jarFile.getEntry("org/springframework/boot/loader/")).isNotNull();
 		}
 	}