Update to JDK 17 (#1394)

Everything still targets JDK 8 (non-records) or JDK 16 (records only)

moshi/build.gradle.kts

@@ -29,9 +29,10 @@ val java16 by sourceSets.creating {
 }
 
 tasks.named<JavaCompile>("compileJava16Java") {
+  // We use JDK 17 for latest but target 16 for maximum compatibility
   javaCompiler.set(
     javaToolchains.compilerFor {
-      languageVersion.set(JavaLanguageVersion.of(16))
+      languageVersion.set(JavaLanguageVersion.of(17))
     }
   )
   options.release.set(16)

moshi/records-tests/build.gradle.kts

@@ -18,7 +18,14 @@ plugins {
   `java-library`
 }
 
+java {
+  toolchain {
+    languageVersion.set(JavaLanguageVersion.of(17))
+  }
+}
+
 tasks.withType<JavaCompile>().configureEach {
+  // Target 16 to ensure minimum compatibility
   options.release.set(16)
 }