Create actual: put top-level actual declarations in the same file

When multiple expect declarations are in the same file,
and some of them already have actual declarations for this platform,
then "Create actual fix" put other declarations into the same file
with existing actual declarations

So #KT-17058 Fixed
So #KT-21082 Fixed

idea/testData/multiModuleQuickFix/functionSameFile/header/header.kt

@@ -0,0 +1,5 @@
+// "Create actual function for platform JVM" "true"
+
+expect fun bar()
+
+expect fun <caret>foo(arg: Int): String