fix(slug): remove all Supplemental Symbols in slug

Fix the `slug` function to remove *all* emojis in the Supplemental
Symbols and Pictographs Unicode block.

I'm not sure why originally only a partial range was removed, but this
change seems to align with GitHub-flavored Markdown.

While this will effectively fix issue #5998, it does not address the
underlying problem where slugs were never designed for widget IDs.

tests/test_slug.py

@@ -25,6 +25,8 @@ from textual._slug import TrackedSlugs, slug
         ("test🙂test", "testtest"),
         ("test🤷test", "testtest"),
         ("test🤷🏻‍♀️test", "testtest"),
+        ("test🤖test", "testtest"),
+        ("test🧠test", "testtest"),
     ],
 )
 def test_simple_slug(text: str, expected: str) -> None: