Build: upgrade language to 1.3 in cli, compiler plugins and Gradle plugin

The language/API version restriction here is to make sure the code works
with Gradle of earlier versions, but all versions of Gradle that we
support already depend on Kotlin 1.3+.

libraries/tools/kotlin-allopen/build.gradle

@@ -24,9 +24,9 @@ dependencies {
 }
 
 tasks.withType(project.compileKotlin.class) {
-    kotlinOptions.languageVersion = "1.2"
-    kotlinOptions.apiVersion = "1.2"
-    kotlinOptions.freeCompilerArgs += ["-Xskip-metadata-version-check"]
+    kotlinOptions.languageVersion = "1.3"
+    kotlinOptions.apiVersion = "1.3"
+    kotlinOptions.freeCompilerArgs += ["-Xskip-prerelease-check"]
 }
 
 jar {
@@ -52,4 +52,4 @@ pluginBundle {
 
 configurePluginMarkers(project)
 
-test.executable = "${JDK_18}/bin/java"
+test.executable = "${JDK_18}/bin/java"