Prepare SwiftUI parser for outputing stylesheet as a map

[NduatiK]

Prepare for liveview-native/live_view_native_stylesheet#86

Prepare ast for conversion to JSON

• Remove variable related code since we are using EEx
• Always return a list of modifiers (instead of the inner tuple for singletons)
• Return annotations as a map instead of keyword list (since empty keywords are treated as lists)

[bcardarella]

I think there was a misunderstanding. We don't need the individual rules output changing at all. Infact I don't think we need any actual changes to how we're generating the stylesheet currently. Instead in live_view_native_stylesheet we simply need to convert the currently generated map to the json object. We can then use https://erlang.org/documentation/doc-15.0-rc3/lib/stdlib-6.0/doc/html/json.html#encode/2 to convert values like tuples that are not generically supported

[NduatiK]

Aah, my bad I wasn't very clear when asking Question 2.

I've created a PR in the stylesheet repo liveview-native/live_view_native_stylesheet#87 and made a few related changes here.

The stylesheeet PR raises the question of whether we should use Jason or :json, the answer to which might require a few small tweaks to the AST to only output arrays.