`AttrValue`'s `PartialEq` takes the enum variant into account

[ranile]

Problem

AttrValue derives PartialEq. That implementation returns false if same string in two different variants is compared.

See #2159

Steps To Reproduce

let a = AttrValue::Owned("same".to_string());
let b = AttrValue::Static("same");
assert_eq!(a.as_ref(), b.as_ref()); // <- equals
assert_eq!(a, b) // <- does not equal

Code snippet taken from #2159

Expected behavior
a and b in above snippet are equal.

assert_eq!(a, b) // <- equals

Screenshots
If applicable, add screenshots to help explain your problem.

Environment:

• Yew version: master
• Rust version: irrelevant
• Target, if relevant: irrelevant
• Build tool, if relevant: irrelevant
• OS, if relevant: irrelevant
• Browser and version, if relevant: irrelevant

Questionnaire

• I'm interested in fixing this myself but don't know where to start
• I would like to fix and I have a solution
• I don't have time to fix this right now, but maybe later

[ranile]

@mibes, if you would like to work on it, feel free to. If you don't want to/can't, no problem, I will PR the fix. Please let me know if you take on it so we don't duplicate work.

[mibes]

@hamza1311 I'm happy to dig into this and do a PR.