breaking: use modern-ast

[dummdidumm]

Transform the code base to use the modern Svelte AST. Requires Svelte 5.

[mustafa0x]

getVisitorKeys: leaveAlone still includes 'Style', but modern AST uses 'StyleSheet'

In src/embed.ts the traversal stoplist contains 'Style' but not 'StyleSheet'.

• In modern AST the code now handles case 'StyleSheet': return embedStyle(true);
• But because 'StyleSheet' isn’t in leaveAlone, Prettier will traverse deep into the CSS AST unnecessarily.

This is probably not correctness-breaking (the embed switch returns null for CSS nodes), but it’s:

• wasted work on big stylesheets, and
• a potential recursion/perf footgun.

Suggested change: add 'StyleSheet' and remove 'Style' (unless deliberately keeping a hybrid path, which this PR otherwise removes).

[l0uisgrange]

Is this really blocking oxc-project/oxc#19807?