[KLIB] Keep "API for KLIB ABI" test data under "compiler/testData/klib/" dir

The test data is used both in ":kotlin-util-klib-abi" and
":native:native.tests" modules. It's better to keep it together with
the test data for other KLIB tests which are also used in more than one
module, i.e. in "compiler/testData/klib/" dir.

compiler/testData/klib/dump-abi/content/root_package.kt

@@ -0,0 +1,17 @@
+// MODULE: root_package_library
+
+// About this test:
+// It checks how declarations from the root package are rendered.
+
+interface Interface {
+    interface NestedInterface
+}
+
+public class Class(val property: String): Interface, Interface.NestedInterface {
+    fun function(): String = ""
+    class NestedClass
+}
+
+fun function(): String = ""
+
+val property: String get() = ""