Do not render declarations from other modules in diagnostic tests

Because PackageViewDescriptor may consist of several package fragments from
different modules (see LazyPackageViewDescriptorImpl#fragments), we now filter
out fragments from irrelevant modules before rendering them into the .txt

compiler/testData/diagnostics/tests/imports/TopLevelClassVsPackage.txt

@@ -47,21 +47,9 @@ public final class a {
 // -- Module: <m3> --
 package
 
-public fun _fun(): kotlin.Unit
 public fun test(/*0*/ a_b: a.b): kotlin.Unit
 public fun test2(/*0*/ _a: a): kotlin.Unit
 public fun test3(/*0*/ _a: a): kotlin.Unit
 
-public final class a {
-    // -- Module: <m2> --
-}
-
 package a {
-    public fun a_fun(): kotlin.Unit
-
-    public final class b {
-        // -- Module: <m1> --
-    }
 }
-
-