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/multimodule/duplicateMethod/sinceKotlin.txt

@@ -21,9 +21,7 @@ public fun test1(): kotlin.Int
 public fun test2(): kotlin.Int
 
 package p1 {
-    @kotlin.SinceKotlin(version = "1.1") public fun foo(/*0*/ s: kotlin.Int): kotlin.String
 }
 
 package p2 {
-    public fun foo(/*0*/ s: kotlin.Int): kotlin.Int
 }