[K/N] Unmute tests already working on native

Also, add issue references for some tests

compiler/testData/codegen/box/extensionFunctions/whenFail.kt

@@ -1,10 +1,4 @@
-// IGNORE_BACKEND: WASM
-// WASM_MUTE_REASON: IGNORED_IN_JS
-// IGNORE_BACKEND: JS_IR
-// IGNORE_BACKEND: JS_IR_ES6
-// TODO: muted automatically, investigate should it be ran for JS or not
-// IGNORE_BACKEND: JS
-// IGNORE_BACKEND: NATIVE
+// TARGET_BACKEND: JVM
 
 fun StringBuilder.takeFirst(): Char {
   if (this.length == 0) return 0.toChar()