jvm-abi-gen: Remove WhenMapping classes from ABI if possible

plugins/jvm-abi-gen/testData/compile/inlineWhenMappings/app/app.kt

@@ -0,0 +1,5 @@
+package app
+
+import lib.*
+
+fun runAppAndReturnOk(): String = value(E.A)

plugins/jvm-abi-gen/testData/compile/inlineWhenMappings/directives.txt

@@ -0,0 +1 @@
+// IGNORE_BACKEND_LEGACY: JVM

plugins/jvm-abi-gen/testData/compile/inlineWhenMappings/lib/lib.kt

@@ -0,0 +1,10 @@
+package lib
+
+enum class E {
+    A, B
+}
+
+inline fun value(x: E) = when (x) {
+    E.A -> "OK"
+    E.B -> "Fail"
+}