[FIR] Extract FirPluginKey into :core:compiler.common and rename it to GeneratedDeclarationKey

This is needed to avoid dependency on :compiler:fir:fir2ir module in
  backend parts of compiler plugins. It will allow to publish those
  parts into jars for IDE, where they are needed for working of debugger
  and bytecode toolwindow

plugins/parcelize/parcelize-compiler/parcelize.backend/build.gradle.kts

@@ -15,7 +15,6 @@ dependencies {
     compileOnly(project(":compiler:backend.jvm"))
     compileOnly(project(":compiler:ir.tree.impl"))
     compileOnly(project(":compiler:fir:tree"))
-    compileOnly(project(":compiler:fir:fir2ir"))
     compileOnly(intellijCore())
     compileOnly(commonDependency("org.jetbrains.intellij.deps:asm-all"))
 }

plugins/parcelize/parcelize-compiler/parcelize.backend/src/org/jetbrains/kotlin/parcelize/ir/ParcelizeFirIrTransformer.kt

@@ -7,9 +7,9 @@ package org.jetbrains.kotlin.parcelize.ir
 
 import org.jetbrains.kotlin.backend.common.extensions.IrPluginContext
 import org.jetbrains.kotlin.descriptors.Modality
-import org.jetbrains.kotlin.fir.backend.IrPluginDeclarationOrigin
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.declarations.IrClass
+import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin.GeneratedByPlugin
 import org.jetbrains.kotlin.ir.declarations.IrModuleFragment
 import org.jetbrains.kotlin.ir.util.companionObject
 import org.jetbrains.kotlin.ir.util.functions
@@ -47,7 +47,7 @@ class ParcelizeFirIrTransformer(
 
         for (function in declaration.functions) {
             val origin = function.origin
-            if (origin !is IrPluginDeclarationOrigin || origin.pluginKey != FirParcelizePluginKey) continue
+            if (origin !is GeneratedByPlugin || origin.pluginKey != FirParcelizePluginKey) continue
             when (function.name.identifier) {
                 ParcelizeSyntheticComponent.ComponentKind.DESCRIBE_CONTENTS.methodName -> {
                     function.generateDescribeContentsBody(parcelableProperties)