refactor(ast): inline AstKind::as_* methods (#5547)

One would hope compiler will inline these trivial methods anyway, but mark them `#[inline]` to make sure.

tasks/ast_tools/src/generators/ast_kind.rs

@@ -161,6 +161,7 @@ impl Generator for AstKindGenerator {
                     format_ident!("as_{}", ident.to_string().to_case(Case::Snake));
                 parse_quote!(
                     ///@@line_break
+                    #[inline]
                     pub fn #snake_case_name(&self) -> Option<&'a #typ> {
                         if let Self::#ident(v) = self {
                             Some(*v)