[POS UI Extensions] Expose navigation stack

[timvandam]

Please list the related package(s)

ui-extensions/point-of-sale

If this related to specific APIs or components, please list them here

https://shopify.dev/docs/api/pos-ui-extensions/2024-10/apis/navigation-api

Is your feature request related to a problem? Please describe.

Being able to access the navigation stack (or at the very least the name of the current Screen) would make POS UI extensions more flexible. I ran into the need to be able to read the stack when creating a POS router; we were forced to wrap the navigation API and Screen component to be able to maintain a copy of the navigation stack. This is redundant but also nontrivial and error prone. I'm running into this same issue again now that I'm creating an improved router

Describe the changes you are looking for

api.navigation.stack // readonly string[]

Describe alternatives you’ve considered

Maintaining a copy of the stack ourselves, as we do now

Additional context