Start a snapshot test for disabled widgets

Eventually this should likely have every user-interactive widget within it.
Perhaps every widget.

tests/snapshot_tests/snapshot_apps/disable_widgets.py

@@ -0,0 +1,58 @@
+from textual.app import App, ComposeResult
+from textual.containers import Vertical
+from textual.widgets import (
+    Header, Footer, Button, DataTable, Input, ListView, ListItem, Label, Tree, TextLog
+)
+
+class WidgetDisableTestApp( App[ None ] ):
+
+    CSS = """
+    DataTable, ListView, Tree {
+        height: 2;
+    }
+    """
+
+    @property
+    def data_table(self) -> DataTable:
+        data_table = DataTable()
+        data_table.add_columns( "Column 1", "Column 2", "Column 3", "Column 4" )
+        data_table.add_rows(
+            [ ( str( n ), str( n * 10 ), str( n * 100 ), str( n * 1000 ) ) for n in range( 100 ) ]
+        )
+        return data_table
+
+    @property
+    def list_view( self ) -> ListView:
+        return ListView(
+            *[ ListItem( Label( f"This is list item {n}" ) ) for n in range( 20 ) ]
+        )
+
+    @property
+    def test_tree( self ) -> Tree:
+        tree = Tree[None]( label="This is a test tree" )
+        for n in range( 10 ):
+            tree.root.add_leaf( f"Leaf {n}" )
+        tree.root.expand()
+        return tree
+
+    def compose( self ) -> ComposeResult:
+        yield Header()
+        yield Vertical(
+            Button(),
+            self.data_table,
+            self.list_view,
+            self.test_tree,
+            TextLog(),
+            Input(),
+            Input(placeholder="This is an empty input with a placeholder"),
+            Input("This is some text in an input"),
+            id="test-container",
+        )
+        yield Footer()
+
+    def on_mount(self) -> None:
+        self.query_one(TextLog).write("Hello, World!")
+        self.query_one("#test-container", Vertical).disabled = True
+
+if __name__ == "__main__":
+    WidgetDisableTestApp().run()