svelte-compiler (Rust port)

This crate ports Svelte compiler parser behavior to typed Rust ASTs.

Porting rules for this branch

• Use typed Rust AST nodes for public parser output (legacy + modern).
• Prefer oxc_* crates for JavaScript/TypeScript parsing, expression parsing, and pattern parsing.
• Match JavaScript Svelte parser fixture output as closely as possible.
• Keep parser paths panic-free in production code; recover or return structured errors instead.
• Preserve existing fixture semantics before introducing new Rust-specific behavior.

Expression and pattern parsing

• Legacy and modern expression parsing routes through OXC whenever possible.
• For ambiguous legacy block/attribute cases, parser recovery falls back to source-slice parsing while still using OXC parse output.
• Type information on snippet parameters is preserved by converting OXC pattern nodes directly into legacy expression nodes.

HTML entity decoding

• Entity decoding is implemented with html-escape for robust named entity support.
• Svelte-compatible semicolon-less decoding behavior is preserved where applicable (for example, &quot before non-alphanumeric boundaries).

Current known parity gaps

• A small set of legacy parser fixtures still differ in malformed-input recovery and comment attachment edge cases.
• Unicode offset parity in some legacy fixtures still needs JS-equivalent index mapping for non-BMP characters.