Refactor inheritMultifileParts to be a JVM analysis flag

Instead of a JVMConfigurationKeys key. This will allow to use it in a
checker in 'frontend.java'

compiler/backend/src/org/jetbrains/kotlin/codegen/MultifileClassCodegen.kt

@@ -25,6 +25,7 @@ import org.jetbrains.kotlin.codegen.context.FieldOwnerContext
 import org.jetbrains.kotlin.codegen.context.MethodContext
 import org.jetbrains.kotlin.codegen.state.GenerationState
 import org.jetbrains.kotlin.config.IncrementalCompilation
+import org.jetbrains.kotlin.config.JvmAnalysisFlags
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.diagnostics.DiagnosticUtils
 import org.jetbrains.kotlin.fileClasses.JvmFileClassUtil
@@ -80,7 +81,7 @@ class MultifileClassCodegenImpl(
                     .filterIsInstance<DeserializedCallableMemberDescriptor>()
 
     private val shouldGeneratePartHierarchy =
-            state.inheritMultifileParts
+        state.languageVersionSettings.getFlag(JvmAnalysisFlags.inheritMultifileParts)
 
     private val partInternalNamesSorted = run {
         val partInternalNamesSet = hashSetOf<String>()

compiler/backend/src/org/jetbrains/kotlin/codegen/state/GenerationState.kt

@@ -227,7 +227,6 @@ class GenerationState private constructor(
     val assertionsMode: JVMAssertionsMode = configuration.get(JVMConfigurationKeys.ASSERTIONS_MODE, JVMAssertionsMode.DEFAULT)
     val isInlineDisabled: Boolean = configuration.getBoolean(CommonConfigurationKeys.DISABLE_INLINE)
     val useTypeTableInSerializer: Boolean = configuration.getBoolean(JVMConfigurationKeys.USE_TYPE_TABLE)
-    val inheritMultifileParts: Boolean = configuration.getBoolean(JVMConfigurationKeys.INHERIT_MULTIFILE_PARTS)
 
     val rootContext: CodegenContext<*> = RootContext(this)