Upgrade Gradle to 8.1 (aws-observability#644)

`./gradlew wrapper --gradle-version 8.1 --distribution-type all`

Also, work through some deprecation warnings.

Author: tylerbenson

java/build.gradle.kts

@@ -8,7 +8,7 @@ allprojects {
     plugins.apply("com.diffplug.spotless")
 
     plugins.withId("java") {
-        configure<JavaPluginConvention> {
+        configure<JavaPluginExtension> {
             sourceCompatibility = JavaVersion.VERSION_1_8
             targetCompatibility = JavaVersion.VERSION_1_8
         }

java/dependencyManagement/build.gradle.kts

@@ -37,7 +37,7 @@ dependencies {
 }
 
 fun isNonStable(version: String): Boolean {
-    val stableKeyword = listOf("RELEASE", "FINAL", "GA").any { version.toUpperCase().contains(it) }
+    val stableKeyword = listOf("RELEASE", "FINAL", "GA").any { version.uppercase().contains(it) }
     val regex = "^[0-9,.v-]+(-r)?$".toRegex()
     val isGuava = version.endsWith("-jre")
     val isStable = stableKeyword || regex.matches(version) || isGuava

java/gradle/wrapper/gradle-wrapper.jar

@@ -1,6 +1,6 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-7.2-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.1-all.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionSha256Sum=f581709a9c35e9cb92e16f585d2c4bc99b2b1a5f85d2badbd3dc6bff59e1e6dd
+distributionSha256Sum=2cbafcd2c47a101cb2165f636b4677fac0b954949c9429c1c988da399defe6a9

java/gradle/wrapper/gradle-wrapper.properties

@@ -28,7 +28,7 @@ tasks {
         from("scripts")
     }
 
-    val assemble by existing {
+    named("assemble") {
         dependsOn(createLayer)
     }
 }

java/layer-javaagent/build.gradle.kts

@@ -30,7 +30,7 @@ tasks {
         from("scripts")
     }
 
-    val assemble by existing {
+    named("assemble") {
         dependsOn(createLayer)
     }
 }