Fix classpath index so entries match those expected by the launcher

This reverts commit ad164269e9 and adds
some additional tests.

Fixes gh-24192

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/resources/org/springframework/boot/gradle/tasks/bundling/BootJarIntegrationTests-explodedApplicationClasspath.gradle

@@ -0,0 +1,25 @@
+plugins {
+	id 'java'
+	id 'org.springframework.boot' version '{version}'
+}
+
+repositories {
+	mavenCentral()
+	maven { url "file:repository" }
+}
+
+dependencies {
+	implementation("com.example:library:1.0-SNAPSHOT")
+	implementation("org.apache.commons:commons-lang3:3.9")
+}
+
+task explode(type: Sync) {
+	dependsOn(bootJar)
+	destinationDir = file("$buildDir/exploded")
+	from zipTree(files(bootJar).singleFile)
+}
+
+task launch(type: JavaExec) {
+	classpath = files(explode)
+	main = 'org.springframework.boot.loader.JarLauncher'
+}

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/resources/org/springframework/boot/gradle/tasks/bundling/BootJarIntegrationTests-packagedApplicationClasspath.gradle

@@ -0,0 +1,19 @@
+
+plugins {
+	id 'java'
+	id 'org.springframework.boot' version '{version}'
+}
+
+task launch(type: JavaExec) {
+	classpath = files(bootJar)
+}
+
+repositories {
+	mavenCentral()
+	maven { url "file:repository" }
+}
+
+dependencies {
+	implementation("com.example:library:1.0-SNAPSHOT")
+	implementation("org.apache.commons:commons-lang3:3.9")
+}