Use 16 as our toolchain, but set release to 8

buildSrc/src/main/kotlin/CommonConfig.kt

@@ -34,7 +34,7 @@
 
     plugins.withId("java") {
         the<JavaPluginExtension>().toolchain {
-            languageVersion.set(JavaLanguageVersion.of(8))
+            languageVersion.set(JavaLanguageVersion.of(16))
         }
     }
 

buildSrc/src/main/kotlin/PlatformConfig.kt

@@ -44,6 +44,7 @@
             val disabledLint = listOf(
                 "processing", "path", "fallthrough", "serial"
             )
+            options.release.set(8)
             options.compilerArgs.addAll(listOf("-Xlint:all") + disabledLint.map { "-Xlint:-$it" })
             options.isDeprecation = true
             options.encoding = "UTF-8"