the trait From<Cow<'_, str>> is not implemented for AttrValue

[Madoshakalaka]

Problem

After merging in #1994 in a project code complains

the trait `From<Cow<'_, str>>` is not implemented for `AttrValue`

Currently these are implemented:

yew/packages/yew/src/virtual_dom/mod.rs

Lines 68 to 84 in 47fad81

	impl From<&'static str> for AttrValue {
	fn from(s: &'static str) -> Self {
	AttrValue::Static(s)
	}
	}
	impl From<String> for AttrValue {
	fn from(s: String) -> Self {
	AttrValue::Owned(s)
	}
	}
	impl From<Rc<str>> for AttrValue {
	fn from(s: Rc<str>) -> Self {
	AttrValue::Rc(s)
	}
	}

Doesn't make sense to omit Cow<'_, str>, as #1994 says

This PR introduces a new type, AttrValue, for attribute values. This is a replacement for Cow<'static, str>

Environment:

• Yew version: [master]

[Madoshakalaka]

Need this:

 impl From<Cow<'static, str>> for AttrValue { 
     fn from(s: Cow<'static, str>) -> Self { 
        match s{
            Cow::Borrowed(s) => {
                s.into()
            }
            Cow::Owned(s) => {
                s.into()
            }
        }
     } 
 } 

[ranile]

This seems like good to have. Would you like to PR it?

[Madoshakalaka]

This seems like good to have. Would you like to PR it?

will do