[JVM_IR]: Improve stepping for when.

Additionally, use the line number of the class for default interface
dispatch methods.

compiler/testData/codegen/bytecodeText/controlStructures/kt17110.kt

@@ -21,6 +21,5 @@ fun infiniteLoop() {
 // 1 GOTO L1
 
 // JVM_IR_TEMPLATES
-// 1 GOTO L6
-// 1 GOTO L7
+// 2 GOTO L6
 // 1 GOTO L0