[Native][tests] Fix file annotation patching in test files

Previously, the test engine was copying @file:OptIn annotations from
each file to all the other files inside the same test data, and also was
removing other file annotations in certain cases.

Now it only adds the opt-ins specified with `!OPT_IN` directives, and
doesn't remove anything.

native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/support/group/ExtTestCaseGroupProvider.kt

@@ -464,19 +464,23 @@ private class ExtTestDataFile(
         val allFileLevelAnnotationsSorted = allFileLevelAnnotations.sorted()
 
         // Finally, make sure that every test file contains all the necessary file-level annotations.
-        if (allFileLevelAnnotationsSorted.isNotEmpty()) {
+        if (testDataFileSettings.optInsForSourceCode.isNotEmpty()) {
             filesToTransform.forEach { handler ->
                 handler.accept(object : KtTreeVisitorVoid() {
                     override fun visitKtFile(file: KtFile) {
                         val oldFileAnnotationList = file.fileAnnotationList
 
                         val newFileAnnotationList = handler.psiFactory.createFile(buildString {
-                            allFileLevelAnnotationsSorted.forEach(::appendLine)
+                            testDataFileSettings.optInsForSourceCode.forEach {
+                                appendLine(getAnnotationText(it))
+                            }
                         }).fileAnnotationList!!
 
                         if (oldFileAnnotationList != null) {
-                            // Replace old annotations list by the new one.
-                            oldFileAnnotationList.replace(newFileAnnotationList).ensureSurroundedByWhiteSpace()
+                            // Add new annotations to the old ones.
+                            newFileAnnotationList.annotationEntries.forEach {
+                                oldFileAnnotationList.add(it).ensureSurroundedByWhiteSpace()
+                            }
                         } else {
                             // Insert the annotations list immediately before package directive.
                             file.addBefore(newFileAnnotationList, file.packageDirective).ensureSurroundedByWhiteSpace()