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/frontend/src/org/jetbrains/kotlin/analyzer/AbstractResolverForProject.kt

@@ -269,6 +269,10 @@ private class DelegatingPackageFragmentProvider<M : ModuleInfo>(
 
         return !packageOracle.packageExists(fqName) && fqName !in syntheticFilePackages
     }
+
+    override fun toString(): String {
+        return "DelegatingProvider for $module in ${resolverForProject.name}"
+    }
 }
 
 private object DiagnoseUnknownModuleInfoReporter {

compiler/frontend/src/org/jetbrains/kotlin/analyzer/common/CommonResolverForModuleFactory.kt

@@ -112,7 +112,10 @@ class CommonResolverForModuleFactory(
                     container.get<MetadataPackageFragmentProvider>()
                 )
 
-        return ResolverForModule(CompositePackageFragmentProvider(packageFragmentProviders), container)
+        return ResolverForModule(
+            CompositePackageFragmentProvider(packageFragmentProviders, "CompositeProvider@CommonResolver for $moduleDescriptor"),
+            container
+        )
     }
 
     companion object {