Compute fix kind from metatadata

[ematipico]

The RuleAction now accepts an applicability field, determining whether the action is safe/unsafe.

However, we also provide the same information to our RuleMeta, which is fix_kind.

Once #2798 is completed, we can retrieve the fix_kind using ctx.metadata().fix_kind.

The idea is to create a method inside FixKind called into_applicability that returns Applicability. This method should panic (use .expect()) if the fix kind isn't provided via macro.

The field applicability should become private (remove pub), however do that at the end. I suggest to create a new method called new inside RuleAction, and then progressively phase out the manual construction of the struct

impl RuleAction {
	pub fn new(category: ActionCategory, applicability: Applicability, message: MarkupBuf, mutation: BatchMutation) -> Self {
		Self {
			category,
			applicability,
			message,
			mutation
		}
	}
}

As a rule, we should have:

        Some(JsRuleAction {
            category: ActionCategory::QuickFix,
            applicability: ctx.metadata().to_applicability(),
            message: markup! { "" }.to_owned(),
            mutation,
        })

[dyc3]

I can pick this up.