Horizontal width auto (#1155)

* Improvements to width:auto HorizontalLayout

* Fix HorizontalLayout.get_content_width

* Horizontal width auto improvement

* Removing some printxz

* Update snapshot for horizontal layout width auto dock

tests/snapshot_tests/snapshot_apps/horizontal_auto_width.py

@@ -0,0 +1,22 @@
+from textual.app import App, ComposeResult
+from textual.containers import Horizontal
+from textual.widgets import Static
+
+
+class HorizontalAutoWidth(App):
+    """
+    Checks that the auto width of the parent Horizontal is correct.
+    """
+    def compose(self) -> ComposeResult:
+        yield Horizontal(
+            Static("Docked left 1", id="dock-1"),
+            Static("Docked left 2", id="dock-2"),
+            Static("Widget 1", classes="widget"),
+            Static("Widget 2", classes="widget"),
+            id="horizontal",
+        )
+
+
+app = HorizontalAutoWidth(css_path="horizontal_auto_width.css")
+if __name__ == '__main__':
+    app.run()