Allow Tab.label to be set and have the display redraw

In support of a better interface for Textualize#3901.

src/textual/widgets/_tabs.py

@@ -5,6 +5,7 @@
 from typing import ClassVar
 
 import rich.repr
+from rich.console import RenderableType
 from rich.style import Style
 from rich.text import Text, TextType
 
@@ -143,6 +144,9 @@ class Disabled(TabMessage):
     class Enabled(TabMessage):
         """A tab was enabled."""
 
+    class Relabelled(TabMessage):
+        """A tab was relabelled."""
+
     def __init__(
         self,
         label: TextType,
@@ -159,9 +163,23 @@ def __init__(
             classes: Space separated list of class names.
             disabled: Whether the tab is disabled or not.
         """
-        self.label = Text.from_markup(label) if isinstance(label, str) else label
         super().__init__(id=id, classes=classes, disabled=disabled)
-        self.update(label)
+        self._label: Text
+        self.label = label
+
+    @property
+    def label(self) -> Text:
+        """The label for the tab."""
+        return self._label
+
+    @label.setter
+    def label(self, label: TextType) -> None:
+        self._label = Text.from_markup(label) if isinstance(label, str) else label
+        self.update(self._label)
+
+    def update(self, renderable: RenderableType = "") -> None:
+        self.post_message(self.Relabelled(self))
+        return super().update(renderable)
 
     @property
     def label_text(self) -> str:
@@ -693,6 +711,11 @@ def _on_tab_enabled(self, event: Tab.Enabled) -> None:
         event.stop()
         self.post_message(self.TabEnabled(self, event.tab))
 
+    def _on_tab_relabelled(self, event: Tab.Relabelled) -> None:
+        """Redraw the highlight when tab is relabelled."""
+        event.stop()
+        self._highlight_active()
+
     def disable(self, tab_id: str) -> Tab:
         """Disable the indicated tab.