Explicitly state that PluginDeclarationProviderFactory is source-only

Before this change `filesScope` was effectively empty in cases when
module info is a library, thus looking
into PackageIndexUtil.packageExists(name, indexedFilesScope, project)
was kind of redundant since it always returns false for empty scopes

The initial motivation was run by 1716720604
that made PackageIndexUtil::packageExists calls much more frequent

idea/ide-common/src/org/jetbrains/kotlin/caches/resolve/JsAnalyzerFacade.kt

@@ -16,7 +16,6 @@
 
 package org.jetbrains.kotlin.idea.caches.resolve
 
-import com.intellij.psi.search.GlobalSearchScope
 import org.jetbrains.kotlin.analyzer.*
 import org.jetbrains.kotlin.caches.resolve.LibraryModuleInfo
 import org.jetbrains.kotlin.config.TargetPlatformVersion
@@ -56,7 +55,7 @@ object JsAnalyzerFacade : AnalyzerFacade() {
             project,
             moduleContext.storageManager,
             syntheticFiles,
-            if (moduleInfo.isLibrary) GlobalSearchScope.EMPTY_SCOPE else moduleContentScope,
+            moduleContentScope,
             moduleInfo
         )