replace 'trait' keyword with 'interface' in library code

libraries/tools/kotlin-gradle-plugin-api/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinGradleSubplugin.kt

@@ -21,7 +21,7 @@ import org.gradle.api.tasks.compile.AbstractCompile
 
 public class SubpluginOption(val key: String, val value: String)
 
-public trait KotlinGradleSubplugin {
+public interface KotlinGradleSubplugin {
     public fun getExtraArguments(project: Project, task: AbstractCompile): List<SubpluginOption>?
     public fun getPluginName(): String
     public fun getGroupName(): String

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/KotlinSourceSet.kt

@@ -6,7 +6,7 @@ import org.gradle.api.internal.file.FileResolver
 import org.gradle.api.internal.file.DefaultSourceDirectorySet
 import org.gradle.util.ConfigureUtil
 
-trait KotlinSourceSet {
+interface KotlinSourceSet {
 
     fun getKotlin(): SourceDirectorySet
     fun kotlin(configureClosure: Closure<Any?>?): KotlinSourceSet

libraries/tools/kotlin-gradle-plugin/src/test/resources/testProject/suppressWarningsAndVersion/src/helloWorld.kt

@@ -7,7 +7,7 @@ fun foo(p: Int??) {
 
 }
 
-trait T {
+interface T {
     abstract fun foo()
 }
 

libraries/tools/kotlin-maven-plugin-test/src/it/test-js-suppressWarnings/src/main/kotlin/org/jetbrains/HelloWorld.kt

@@ -7,7 +7,7 @@ fun foo(p: Int??) {
 
 }
 
-trait T {
+interface T {
     abstract fun foo()
 }
 

libraries/tools/kotlin-maven-plugin-test/src/it/test-suppressWarnings/src/main/kotlin/org/jetbrains/HelloWorld.kt

@@ -7,7 +7,7 @@ fun foo(p: Int??) {
 
 }
 
-trait T {
+interface T {
     abstract fun foo()
 }
 

libraries/tools/kotlin-stdlib-gen/src/generators/GenerateJavaScriptStubs.kt

@@ -87,7 +87,7 @@ $imports
             val interfaces = klass.getInterfaces()
             val extends = if (interfaces != null && interfaces.size == 1) ": ${interfaces[0]?.getSimpleName()}" else ""
 
-            println("native public trait ${klass.getSimpleName()}$extends {")
+            println("native public interface ${klass.getSimpleName()}$extends {")
 
             val methods = klass.getDeclaredMethods().sortBy { it.getName()!! }
             if (methods != null) {