fix: parse type assertions (#1)

Does so by not parsing as JSX by default (this is a breaking change if you would switch to this parser from acorn-typescript)

Fixes sveltejs/svelte#13179
Fixes TyrealHu/acorn-typescript#58

Author: dummdidumm

.changeset/common-states-cut.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/acorn-typescript': patch
+---
+
+fix: parse type assertions