Rename: Warn about function name conflicts

#KT-13239 Fixed

idea/testData/refactoring/rename/topLevelFunctionRedeclaration/before/test/test.kt

@@ -0,0 +1,9 @@
+package test
+
+fun /*rename*/namedFunA() {}
+fun namedFunB() {}
+
+fun useNames() {
+    namedFunA()
+    namedFunB()
+}

idea/testData/refactoring/rename/topLevelFunctionRedeclaration/topLevelFunctionRedeclaration.test

@@ -0,0 +1,7 @@
+{
+  "type": "MARKED_ELEMENT",
+  "mainFile": "test/test.kt",
+  "newName": "namedFunB",
+  "withRuntime": "true",
+  "hint": "Function 'namedFunB' is already declared in package 'test'"
+}