New J2K: make post-processing aware of other files which are being converted

Before post-processing was able to handle only one converting file at once
So, some conversions (like (field, getter, setter) to Kotlin property)
was not able to work when converting class hierarchy was split into
multiple files.
Also, inferring nullability for a set of files was broken

#KT-19569 fixed
#KT-34266 fixed
#KT-32518 fixed

idea/idea-j2k/src/org/jetbrains/kotlin/idea/j2k/J2kPostProcessor.kt

@@ -32,8 +32,7 @@ import org.jetbrains.kotlin.idea.core.util.range
 import org.jetbrains.kotlin.idea.util.ImportInsertHelper
 import org.jetbrains.kotlin.idea.util.application.runReadAction
 import org.jetbrains.kotlin.idea.util.application.runWriteAction
-import org.jetbrains.kotlin.j2k.ConverterContext
-import org.jetbrains.kotlin.j2k.PostProcessor
+import org.jetbrains.kotlin.j2k.*
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.psi.KtElement
 import org.jetbrains.kotlin.psi.KtFile
@@ -61,11 +60,15 @@ class J2kPostProcessor(private val formatCode: Boolean) : PostProcessor {
     }
 
     override fun doAdditionalProcessing(
-        file: KtFile,
+        target: JKPostProcessingTarget,
         converterContext: ConverterContext?,
-        rangeMarker: RangeMarker?,
         onPhaseChanged: ((Int, String) -> Unit)?
-    ) =
+    ) {
+        val (file, rangeMarker) = when (target) {
+            is JKPieceOfCodePostProcessingTarget -> target.file to target.rangeMarker
+            is JKMultipleFilesPostProcessingTarget -> target.files.single() to null
+        }
+
         runBlocking(EDT.ModalityStateElement(ModalityState.defaultModalityState())) {
             do {
                 var modificationStamp: Long? = file.modificationStamp
@@ -109,7 +112,7 @@ class J2kPostProcessor(private val formatCode: Boolean) : PostProcessor {
                 }
             }
         }
-
+    }
 
     private data class ActionData(val element: KtElement, val action: () -> Unit, val priority: Int, val writeActionNeeded: Boolean)
 

idea/src/org/jetbrains/kotlin/idea/actions/JavaToKotlinAction.kt

@@ -57,7 +57,6 @@ import org.jetbrains.kotlin.idea.util.isRunningInCidrIde
 import org.jetbrains.kotlin.j2k.*
 import org.jetbrains.kotlin.psi.KtFile
 import org.jetbrains.kotlin.psi.UserDataProperty
-import org.jetbrains.kotlin.utils.addToStdlib.safeAs
 import java.io.File
 import java.io.IOException
 import java.util.*