feat: render docs from aliased type when type has no docs

[dqkqd]

Trying to close #18344

• Find the docs by traversing upwards if the type itself has none but aliasing for another type that might have.
• Show docs from aliased type.
• Showing description that we are displaying documentation for different definition in hover box.

[Veykril]

We should go through the HIR here instead of doing a syntactic walk, something like

if let Definition::TypeAlias(type_alias) = def {
    if docs.is_some() {
        return docs;
    }
	if let Some(adt) = type_alias.ty(db).as_adt() {
    	return adt.docs(db, famous_desf, edition);
    }
}

This means we miss intermediate aliases but that is fine, we don't handle those with most things due to how the type system erases them.

[dqkqd]

Thanks, I fixed it.
Should have looked at the implementation in def.docs, rather than walking syntactically. :(

[Veykril]

Thanks!
@bors r+

[bors]

📌 Commit 44e48d7 has been approved by Veykril

It is now in the queue for this repository.

[bors]

⌛ Testing commit 44e48d7 with merge eddab6e...

[bors]

☀️ Test successful - checks-actions
Approved by: Veykril
Pushing eddab6e to master...