add prop(attrs) extra attributes to relevant top level elements of components

[Panaetius]

I really like the DatePicker, but I want to add a label for it with the <label for="id"> tag. For this the input of the datepicker would need to have a corresponding id and there's currently no way to add that.

Leptos supports passing in dynamic attributes like

#[component]
pub fn DatePicker(
    #[prop(optional, into)] value: RwSignal<Option<NaiveDate>>,
    #[prop(optional, into)] class: MaybeSignal<String>,
+    #[prop(attrs)] attrs: Vec<(&'static str, Attribute)>,
) -> impl IntoView {
    [...]
-    <Input class value=show_date_text on_focus=open_panel on_blur=on_input_blur>
+    <Input class value=show_date_text on_focus=open_panel on_blur=on_input_blur {..attrs}>
    [...]

which can then be used like

<DatePicker value=... attr:id=my-id />

i.e. it allows to pass in arbitrary settings to a component. Of course with some components it's not clear which HTML tag should get the attributes, but for the DatePicker I think the input field makes sense. It also allows setting other things like alt text, maxLength etc. That should be much easier than adding manual support for all the various properties.

In general it'd be nice to add this on all components (not just DatePicker) where it makes sense, it'd make them much more reusable.

[luoxiaozero]

Looking good, we can start by adding the Input component and its associated components.

[luoxiaozero]

Added, please see #65 for details.

[Panaetius]

awesome, thank you so much! just tested it and can confirm it works