[PyCharm] PY-77218 Jupyter bugfix - don't show add cells toolbar at the end of the console + minor refactoring

(cherry picked from commit bff263fb3c7131180d80e44cae52f9ff39fc27c3)

GitOrigin-RevId: ebf47b6024e1178a6d9b2fb3421285a3761856b0

notebooks/visualization/src/com/intellij/notebooks/visualization/NotebookCellInlayManager.kt

@@ -2,6 +2,7 @@ package com.intellij.notebooks.visualization
 
 import com.intellij.ide.ui.LafManagerListener
 import com.intellij.notebooks.ui.isFoldingEnabledKey
+import com.intellij.notebooks.ui.visualization.NotebookBelowLastCellPanel
 import com.intellij.notebooks.visualization.inlay.JupyterBoundsChangeHandler
 import com.intellij.notebooks.visualization.ui.*
 import com.intellij.notebooks.visualization.ui.EditorCellEventListener.*
@@ -23,6 +24,7 @@ import com.intellij.openapi.editor.ex.EditorEx
 import com.intellij.openapi.editor.ex.FoldingListener
 import com.intellij.openapi.editor.ex.FoldingModelEx
 import com.intellij.openapi.editor.impl.EditorImpl
+import com.intellij.openapi.editor.Inlay
 import com.intellij.openapi.util.Disposer
 import com.intellij.openapi.util.Key
 import com.intellij.openapi.util.registry.Registry
@@ -48,6 +50,8 @@ class NotebookCellInlayManager private constructor(
 
   val views = mutableMapOf<EditorCell, EditorCellView>()
 
+  private var belowLastCellInlay: Inlay<*>? = null
+
   /**
    * Listens for inlay changes (called after all inlays are updated). Feel free to convert it to the EP if you need another listener
    */
@@ -183,6 +187,7 @@ class NotebookCellInlayManager private constructor(
 
     setupFoldingListener()
     setupSelectionUI()
+    addBelowLastCellInlay()
 
     cellEventListeners.addListener(object : EditorCellEventListener {
       override fun onEditorCellEvents(events: List<EditorCellEvent>) {
@@ -275,6 +280,21 @@ class NotebookCellInlayManager private constructor(
     }
   }
 
+  private fun addBelowLastCellInlay() {  // PY-77218
+    belowLastCellInlay = editor.addComponentInlay(
+      NotebookBelowLastCellPanel(editor),
+      isRelatedToPrecedingText = true,
+      showAbove = false,
+      priority = 0,
+      offset = editor.document.getLineEndOffset((editor.document.lineCount - 1).coerceAtLeast(0))
+    )
+  }
+
+  fun removeBelowLastCellInlay() {
+    belowLastCellInlay?.dispose()
+    belowLastCellInlay = null
+  }
+
   private fun setupFoldingListener() {
     val foldingModel = editor.foldingModel
     foldingModel.addListener(object : FoldingListener {

notebooks/visualization/src/com/intellij/notebooks/visualization/ui/NotebookEditorUiUtil.kt

@@ -1,6 +1,5 @@
 package com.intellij.notebooks.visualization.ui
 
-import com.intellij.openapi.application.ReadAction
 import com.intellij.openapi.application.WriteIntentReadAction
 import com.intellij.openapi.editor.Editor
 import com.intellij.openapi.editor.EditorKind