Force justify left on text input

Author: darrenburns

src/textual/widgets/_input.py

@@ -171,7 +171,7 @@ def cursor_width(self) -> int:
 
     def render(self) -> RenderableType:
         if not self.value:
-            placeholder = Text(self.placeholder)
+            placeholder = Text(self.placeholder, justify="left")
             placeholder.stylize(self.get_component_rich_style("input--placeholder"))
             if self.has_focus:
                 cursor_style = self.get_component_rich_style("input--cursor")