[FIR] Add ability to generate companion object from compiler plugin

compiler/fir/entrypoint/src/org/jetbrains/kotlin/fir/session/FirSessionFactory.kt

@@ -167,6 +167,7 @@ object FirSessionFactory {
             }.configure()
 
             val dependenciesSymbolProvider = FirDependenciesSymbolProviderImpl(this)
+            val generatedSymbolsProvider = FirExtensionDeclarationsSymbolProvider.create(this)
             register(
                 FirSymbolProvider::class,
                 FirCompositeSymbolProvider(
@@ -174,13 +175,15 @@ object FirSessionFactory {
                     listOfNotNull(
                         firProvider.symbolProvider,
                         symbolProviderForBinariesFromIncrementalCompilation,
-                        FirExtensionDeclarationsSymbolProvider.create(this),
+                        generatedSymbolsProvider,
                         JavaSymbolProvider(this, projectEnvironment.getFirJavaFacade(this, moduleData, scope)),
                         dependenciesSymbolProvider,
                     )
                 )
             )
 
+            generatedSymbolsProvider?.let { register(FirExtensionDeclarationsSymbolProvider::class, it) }
+
             register(
                 FirDependenciesSymbolProvider::class,
                 dependenciesSymbolProvider