Added support of external serializers to the FIR

Co-authored-by: Leonid Startsev <leonid.startsev@jetbrains.com>
Merge-request: KT-MR-7334
Merged-by: Sergey Shanshin <Sergey.Shanshin@jetbrains.com>

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/extensions/IrPluginContext.kt

@@ -34,6 +34,11 @@ annotation class FirIncompatiblePluginAPI(val hint: String = "")
 interface IrPluginContext : IrGeneratorContext {
     val languageVersionSettings: LanguageVersionSettings
 
+    /**
+     * Indicates that the plugin works after FIR. Effectively it means that all descriptor-based API may contain incorrect and/or incomplete information, and declarations marked with `@FirIncompatibleApi` will throw runtime exceptions.
+     */
+    val afterK2: Boolean
+
     @ObsoleteDescriptorBasedAPI
     val moduleDescriptor: ModuleDescriptor
 

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/extensions/IrPluginContextImpl.kt

@@ -42,6 +42,8 @@ open class IrPluginContextImpl constructor(
     override val symbols: BuiltinSymbolsBase = BuiltinSymbolsBase(irBuiltIns, st)
 ) : IrPluginContext {
 
+    override val afterK2: Boolean = false
+
     override val platform: TargetPlatform? = module.platform
 
     @OptIn(ObsoleteDescriptorBasedAPI::class)