Platform header annotator: implementation + simple multi-platform highlighting tests #KT-14905 Fixed

idea/testData/multiModuleHighlighting/platform4/header/header.kt

@@ -0,0 +1,23 @@
+header class <error>My</error> {
+
+    fun foo(): Int
+
+    fun bar(arg: Int): Boolean
+
+}
+
+header class <error>Your</error> {
+
+    fun foo(): Int
+
+    fun bar(arg: Int): Boolean
+
+}
+
+header class His {
+
+    fun foo(): Int
+
+    fun bar(arg: Int): Boolean
+
+}