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

idea/testData/quickfix/createFromUsage/createClass/referenceExpression/traitByQualifier.kt.after

@@ -1,9 +1,9 @@
-// "Create trait 'A'" "true"
+// "Create interface 'A'" "true"
 // ERROR: Unresolved reference: B
 package p
 
 fun foo() = A.B
 
-trait A {
+interface A {
 
 }