[FIR] Add compiler extension for plugin registration

compiler/cli/cli-common/resources/META-INF/extensions/compiler.xml

@@ -62,5 +62,7 @@
                         interface="com.intellij.ide.util.projectWizard.ModuleBuilder"/>
         <extensionPoint qualifiedName="org.jetbrains.kotlin.renameHandler"
                         interface="com.intellij.refactoring.rename.RenameHandler"/>
+        <extensionPoint qualifiedName="org.jetbrains.kotlin.fir.extensions.FirExtensionRegistrarExtension"
+                        interface="org.jetbrains.kotlin.fir.extensions.FirExtensionRegistrarExtension"/>
     </extensionPoints>
 </idea-plugin>

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/extensions/FirExtensionRegistrarExtension.kt

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.fir.extensions
+
+import org.jetbrains.kotlin.extensions.ProjectExtensionDescriptor
+
+abstract class FirExtensionRegistrarExtension {
+    companion object : ProjectExtensionDescriptor<FirExtensionRegistrarExtension>(
+        "org.jetbrains.kotlin.fir.frontendIrExtensionRegistrarExtension",
+        FirExtensionRegistrarExtension::class.java
+    )
+
+    protected inner class ExtensionRegistrarContext
+
+    protected abstract fun ExtensionRegistrarContext.configurePlugin()
+
+    fun configure(): RegisteredExtensions {
+        ExtensionRegistrarContext().configurePlugin()
+        return RegisteredExtensions()
+    }
+
+    class RegisteredExtensions
+}
+
+fun FirExtensionPointService.registerExtensions(extensions: FirExtensionRegistrarExtension.RegisteredExtensions) {}