[css-view-transitions-2] @view-transition resolution algorithm should cascade

The @view-transition resolution algorithm is currently specifies:

To get the resolve @view-transition rule for a Document document:

1. Let matchingRule be the last @view-transition rule in document which has a navigation descriptor whose computed value is auto.
2. If matchingRule is not found, then return "not found".
3. Return a list of strings corresponding to that descriptor’s computed value.

But I think it needs to account for the CSS cascade. Take this example:

<style>
  @view-transition {
    navigation: auto;
    type: foo;
  }

  @import url('style.css') layer(A);
</style>

  /*style.css*/
  @view-transition {
    navigation: auto;
    type: bar;
  }

I would expect the foo transition to be resolved, despite the fact that the bar transition is "last".

I think the way to do this will be to keep a map of all encountered @view-transition rules, keyed by their matcher descriptors (currently just navigation but later including from, to, etc. with succeeding levels of the cascade overriding a entries where the matchers are equal.

While we're here:

Return a list of strings corresponding to that descriptor’s computed value.

I'm assuming "that descriptor" is navigation?

Start with the CSS View Transitions 2 section on resolving the @view-transition rule and compare its current last-rule behavior with the CSS cascade example in the issue. Clarify whether the descriptor is navigation, then update the algorithm so the documented result matches the intended cascade semantics.