Add multi-file tests for primitive completion

- This is required to test/debug correct completion from imports

idea/idea-completion/testData/basic/multifilePrimitive/NestedClassImport/NestedClassImport.dependency.kt

@@ -0,0 +1,7 @@
+package dependency
+
+class TopLevelClass {
+    class NestedClass
+
+    inner class InnerClass
+}

idea/idea-completion/testData/basic/multifilePrimitive/NestedClassImport/NestedClassImport.kt

@@ -0,0 +1,8 @@
+import dependency.TopLevelClass.*
+
+fun usage() {
+    <caret>
+}
+
+// EXIST: NestedClass
+// EXIST: InnerClass