Auto implementation panics when raw identifiers are used for fallback function name

[ironcev]

E.g, this program:

contract;

#[fallback]
fn r#fn() {
}

panics with:

thread 'main' panicked at sway-core/src/semantic_analysis/ast_node/declaration/auto_impl/mod.rs:70:9:
Handler { inner: RefCell { value: HandlerInner { errors: [Parse { error: ParseError { span: Span { src (ptr): 0x5589ff417930, source_id: Some(SourceId(1048669)), start: 211, end: 213, as_str(): "fn" }, kind: ReservedKeywordIdentifier } }], warnings: [] } } }