Add debug strings to frontend scopes-related structures

Such as:
- PackageFragmentProviders, and, in particular,
CompositePackageFragmentProviders
- JavaPackageFragments
- Scopes produced by those providers

The rationale is that a lot of frontend-facing bugs (like red code) are
easily recognizeable in resolution. But at that point you just see a
bunch of scopes, without meaningful toStrings, you don't know who has
produced them, and what's exactly wrong.

With this commit it should make debugging slightly easier: now at least
you'll be able to see that "this scope is a scope of package fragment
for foo.bar of module baz" and decide whether the declaration should or
should not have been resolved from such scope.

compiler/tests-common/tests/org/jetbrains/kotlin/checkers/AbstractDiagnosticsTest.kt

@@ -437,7 +437,8 @@ abstract class AbstractDiagnosticsTest : BaseDiagnosticsTest() {
                 listOf(
                     container.get<KotlinCodeAnalyzer>().packageFragmentProvider,
                     container.get<JavaDescriptorResolver>().packageFragmentProvider
-                )
+                ),
+                "CompositeProvider@AbstractDiagnosticsTest for $moduleDescriptor"
             )
         )