X-Ray: enable in .mill files, #SCL-24263 fixed

(cherry picked from commit e195364)

Author: pavelfatin

scala/codeInsight/src/org/jetbrains/plugins/scala/codeInsight/hints/ScalaEditorFactoryListener.scala

@@ -49,7 +49,7 @@ class ScalaEditorFactoryListener extends EditorFactoryListener {
 
   override def editorCreated(event: EditorFactoryEvent): Unit = {
     val file = event.getEditor.getVirtualFile
-    if (file == null || file.getExtension != "scala" && file.getExtension != "sc" && file.getExtension != "sbt") return
+    if (file == null || file.getExtension != "scala" && file.getExtension != "sc" && file.getExtension != "sbt" && file.getExtension != "mill") return
 
     val component = event.getEditor.getContentComponent
     component.addFocusListener(editorFocusListener)

scala/codeInsight/src/org/jetbrains/plugins/scala/codeInsight/hints/XRayModeWidgetActionProvider.scala

@@ -33,7 +33,7 @@ class XRayModeWidgetActionProvider extends InspectionWidgetActionProvider {
     if (project == null || project.isDefault) return null
 
     val file = editor.getVirtualFile
-    if (file == null || file.getExtension != "scala" && file.getExtension != "sc" && file.getExtension != "sbt") return null
+    if (file == null || file.getExtension != "scala" && file.getExtension != "sc" && file.getExtension != "sbt" && file.getExtension != "mill") return null
 
     val action = new DumbAwareAction(ScalaCodeInsightBundle.message("xray.mode.widget.text")) with CustomComponentAction {
       override def getActionUpdateThread: ActionUpdateThread = ActionUpdateThread.EDT

scala/codeInsight/src/org/jetbrains/plugins/scala/codeInsight/implicits/MouseHandler.scala

@@ -167,7 +167,7 @@ private final class MouseHandler extends ProjectActivity {
 
     def isScalaFile = {
       val file = e.getEditor.getVirtualFile
-      file != null && (file.getExtension == "scala" || file.getExtension == "sc" || file.getExtension == "sbt")
+      file != null && (file.getExtension == "scala" || file.getExtension == "sc" || file.getExtension == "sbt" || file.getExtension == "mill")
     }
 
     def checkSettings = {

scala/scala-impl/src/org/jetbrains/plugins/scala/incremental/package.scala

@@ -44,5 +44,5 @@ package object incremental {
   }
 
   private[incremental] def isScalaIn(file: VirtualFile): Boolean =
-    file != null && (file.getExtension == "scala" || file.getExtension == "sc" || file.getExtension == "sbt")
+    file != null && (file.getExtension == "scala" || file.getExtension == "sc" || file.getExtension == "sbt" || file.getExtension == "mill")
 }