Remove TreeNode as a pseudo-widget

This encourages importing it from `textual.widgets.tree` instead, keeping it
in line with the other changes made for #1637.

Note this is a breaking change.

examples/json_tree.py

@@ -4,7 +4,8 @@ from pathlib import Path
 from rich.text import Text
 
 from textual.app import App, ComposeResult
-from textual.widgets import Header, Footer, Tree, TreeNode
+from textual.widgets import Header, Footer, Tree
+from textual.widgets.tree import TreeNode
 
 
 class TreeApp(App):

src/textual/widgets/__init__.py

@@ -23,7 +23,6 @@ if typing.TYPE_CHECKING:
     from ._static import Static
     from ._text_log import TextLog
     from ._tree import Tree
-    from ._tree_node import TreeNode
     from ._welcome import Welcome
     from ..widget import Widget
 
@@ -44,7 +43,6 @@ __all__ = [
     "Static",
     "TextLog",
     "Tree",
-    "TreeNode",
     "Welcome",
 ]
 

src/textual/widgets/_tree_node.py

@@ -1 +0,0 @@
-from ._tree import TreeNode as TreeNode

tests/tree/test_tree_node_children.py

@@ -1,5 +1,6 @@
 import pytest
-from textual.widgets import Tree, TreeNode
+from textual.widgets import Tree
+from textual.widgets.tree import TreeNode
 
 
 def label_of(node: TreeNode[None]):

tests/tree/test_tree_node_label.py

@@ -1,4 +1,5 @@
-from textual.widgets import Tree, TreeNode
+from textual.widgets import Tree
+from textual.widgets.tree import TreeNode
 from rich.text import Text
 
 

tests/tree/test_tree_node_parent.py

@@ -1,4 +1,4 @@
-from textual.widgets import TreeNode, Tree
+from textual.widgets import Tree
 
 
 def test_tree_node_parent() -> None: