Do not force loading all kt-files inside LazyPackageDescriptor constructor

Effectively it leads to all stubs being built for any once used package

The idea is that they only were used for FILE_TO_PACKAGE_FRAGMENT
that is mostly read in backend and rarely in the IDE, so we can replace
its usages with searching through related package-fragments

idea/idea-analysis/src/org/jetbrains/kotlin/idea/stubindex/resolve/StubBasedPackageMemberDeclarationProvider.kt

@@ -109,6 +109,10 @@ class StubBasedPackageMemberDeclarationProvider(
         return PackageIndexUtil.findFilesWithExactPackage(fqName, searchScope, project)
     }
 
+    override fun containsFile(file: KtFile): Boolean {
+        return searchScope.contains(file.virtualFile ?: return false)
+    }
+
     override fun getTypeAliasDeclarations(name: Name): Collection<KtTypeAlias> {
         return KotlinTopLevelTypeAliasFqNameIndex.getInstance().get(childName(name), project, searchScope)
     }