Quick-fix for header without implementation + a set of tests #KT-14908 Fixed

idea/testData/multiModuleQuickFix/function/header/header.kt

@@ -0,0 +1,3 @@
+// "Create header function implementation for platform JVM" "true"
+
+header fun <caret>foo(arg: Int): String

idea/testData/multiModuleQuickFix/function/header/header.kt.after

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+// "Create header function implementation for platform JVM" "true"
+
+header fun foo(arg: Int): String

idea/testData/multiModuleQuickFix/function/jvm/foo.kt

@@ -0,0 +1 @@
+// foo: to be implemented

idea/testData/multiModuleQuickFix/function/jvm/foo.kt.after

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+// foo: to be implemented
+impl fun foo(arg: Int): String {
+    TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
+}