replace 'trait' keyword with 'interface' in user-visible messages and code generation tools

compiler/testData/diagnostics/tests/duplicateJvmSignature/functionAndProperty/trait.txt

@@ -1,6 +1,6 @@
 package
 
-internal trait T {
+internal interface T {
     internal open val x: kotlin.Int
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     internal open fun getX(): kotlin.Int

compiler/testData/diagnostics/tests/duplicateJvmSignature/functionAndProperty/withErrorTypes.txt

@@ -1,6 +1,6 @@
 package
 
-internal trait T {
+internal interface T {
     internal abstract val x: [ERROR : ErrorType]
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     internal abstract fun getX(): [ERROR : ErrorType1]