[Plugins] Introduce new API for registering compiler plugins

Original `ComponentRegistrar` exposes Project to its registration method,
  so plugins should manually register extensions to it. To prepare for
  possible unbound compiler from Project API in future new  `K2ComponentRegistrar`
  introduced which provides registration method without Project at all

plugins/atomicfu/atomicfu-compiler/src/org/jetbrains/kotlinx/atomicfu/compiler/extensions/AtomicfuComponentRegistrar.kt

@@ -16,22 +16,21 @@
 
 package org.jetbrains.kotlinx.atomicfu.compiler.extensions
 
-import com.intellij.mock.MockProject
-import com.intellij.openapi.project.Project
 import org.jetbrains.kotlin.backend.common.extensions.IrGenerationExtension
-import org.jetbrains.kotlin.compiler.plugin.ComponentRegistrar
+import org.jetbrains.kotlin.compiler.plugin.CompilerPluginRegistrar
 import org.jetbrains.kotlin.config.CompilerConfiguration
 
-class AtomicfuComponentRegistrar : ComponentRegistrar {
-    override fun registerProjectComponents(project: MockProject, configuration: CompilerConfiguration) {
-        registerExtensions(project)
+class AtomicfuComponentRegistrar : CompilerPluginRegistrar() {
+    override fun ExtensionStorage.registerExtensions(configuration: CompilerConfiguration) {
+        Companion.registerExtensions(this)
     }
 
     override val supportsK2: Boolean
         get() = true
 
     companion object {
-        fun registerExtensions(project: Project) {
-            IrGenerationExtension.registerExtension(project, AtomicfuLoweringExtension()) }
+        fun registerExtensions(extensionStorage: ExtensionStorage) = with(extensionStorage) {
+            IrGenerationExtension.registerExtension(AtomicfuLoweringExtension())
+        }
     }
 }

plugins/atomicfu/atomicfu-compiler/test/org/jetbrains/kotlinx/atomicfu/AbstractAtomicfuJsIrTest.kt

@@ -34,7 +34,7 @@ open class AbstractAtomicfuJsIrTest : AbstractJsIrTest(
 }
 
 class AtomicfuEnvironmentConfigurator(testServices: TestServices) : EnvironmentConfigurator(testServices) {
-    override fun registerCompilerExtensions(project: Project, module: TestModule, configuration: CompilerConfiguration) {
+    override fun legacyRegisterCompilerExtensions(project: Project, module: TestModule, configuration: CompilerConfiguration) {
         IrGenerationExtension.registerExtension(project, AtomicfuLoweringExtension())
     }
 }

plugins/atomicfu/atomicfu-compiler/test/org/jetbrains/kotlinx/atomicfu/AbstractAtomicfuJvmIrTest.kt

@@ -11,6 +11,8 @@ import org.jetbrains.kotlin.cli.jvm.compiler.KotlinCoreEnvironment
 import org.jetbrains.kotlin.cli.jvm.config.JvmClasspathRoot
 import org.jetbrains.kotlin.cli.jvm.config.addJvmClasspathRoots
 import org.jetbrains.kotlin.codegen.AbstractAsmLikeInstructionListingTest
+import org.jetbrains.kotlin.compiler.plugin.CompilerPluginRegistrar
+import org.jetbrains.kotlin.compiler.plugin.CompilerPluginRegistrar.ExtensionStorage
 import org.jetbrains.kotlin.config.CompilerConfiguration
 import org.jetbrains.kotlin.test.TargetBackend
 import org.jetbrains.kotlin.test.builders.TestConfigurationBuilder
@@ -53,8 +55,8 @@ private fun TestConfigurationBuilder.configureForKotlinxAtomicfu(librariesPaths:
                     configuration.addJvmClasspathRoots(librariesPaths)
                 }
 
-                override fun registerCompilerExtensions(project: Project, module: TestModule, configuration: CompilerConfiguration) {
-                    AtomicfuComponentRegistrar.registerExtensions(project)
+                override fun ExtensionStorage.registerCompilerExtensions(module: TestModule, configuration: CompilerConfiguration) {
+                    AtomicfuComponentRegistrar.registerExtensions(this)
                 }
             }
         })