Avoid creating `AnimationValue` to decide whether to start a transition

[Loirooriol]

stylo/style/servo/animation.rs

Lines 1059 to 1063 in 51593b0

	let Some(from) = AnimationValue::from_computed_values(*property_declaration_id, old_style)
	else {
	return;
	};
	let Some(to) = AnimationValue::from_computed_values(*property_declaration_id, new_style)

Gecko uses a different logic, but it optimized this kind of thing in https://phabricator.services.mozilla.com/D283849, improving speedometer3 results.