Add border_title and border_subtitle as kwargs to Widget constructor

[davetapley]

Currently you can set border_title like this:

textual/docs/examples/guide/widgets/hello06.py

Lines 23 to 26 in cb61239

	class Hello(Static):
	"""Display a greeting."""
	BORDER_TITLE = "Hello Widget" # (1)!

Or like this:

textual/docs/examples/styles/border_title_colors.py

Lines 11 to 13 in cb61239

	def on_mount(self) -> None:
	label = self.query_one(Label)
	label.border_title = "Textual Rocks"

---

I have a third use-case where I'd like to set it on a Container. Inspired by this I came up with:

def title_container(border_title: str, *args: Any, **kwargs: Any) -> Container:
    container = Container(*args, **kwargs)
    container.border_title = border_title
    return container

Use like this:

        collection = title_container("Collection", classes="section")
        with collection:
            yield Select(options, allow_blank=False)

---

But then it occurred to me that this would (I think) be nicer:

        with Collection(classes="section", border_title="Collection"):
            yield Select(options, allow_blank=False)

Any thoughts / concerns? Happy to have a go at a PR.

[davep]

I'm pretty sure this has come up before and we've resisted this as it adds even more keyword arguments to the already-busy constructor of every widget that defines its own __init__.

For what it's worth, the pattern I use is this:

with Collection(classes="section") as collection:
    collection.border_title="Collection"
    yield Select(options, allow_blank=False)

Or, where it's been more useful, I've even taken to having a title utility function:

with title(Collection(classes="section"), "Collection"):
    yield Select(options, allow_blank=False)

where title is something like:

def title(widget: Widget, title: str) -> Widget:
    widget.border_title = title
    return widget

[davetapley]

Thanks! I can't believe I didn't think to do the as version. I like that ✅