Test infra: refactor IGNORE_BACKEND directive

treat it as a general one, introduce *_K1 and *_K2 variants for
more specific ignoring

compiler/testData/debug/stepping/kt15259.kt

@@ -1,5 +1,4 @@
 // IGNORE_BACKEND: JVM_IR
-// IGNORE_BACKEND_FIR: JVM_IR
 // FILE: test.kt
 interface ObjectFace
 
@@ -15,16 +14,16 @@ fun box() {
 // IR backend has additional steps on the way _out_ of the init block.
 
 // EXPECTATIONS JVM JVM_IR
+// test.kt:11 box
+// test.kt:5 makeFace
+// test.kt:5 <init>
+// test.kt:7 <init>
+// test.kt:8 makeFace
+// test.kt:11 box
 // test.kt:12 box
-// test.kt:6 makeFace
-// test.kt:6 <init>
-// test.kt:8 <init>
-// test.kt:9 makeFace
-// test.kt:12 box
-// test.kt:13 box
 
 // EXPECTATIONS JS_IR
-// test.kt:12 box
-// test.kt:9 makeFace
-// test.kt:6 <init>
-// test.kt:13 box
+// test.kt:11 box
+// test.kt:8 makeFace
+// test.kt:5 <init>
+// test.kt:12 box