Properly parse 'as const'

Author: guillaumebrunerie

common/corpus/declarations.txt

@@ -457,6 +457,7 @@ Type casts
 
 foo as any as Array<number>
 bar satisfies number[]
+"foobar" as const
 
 ---
 
@@ -466,7 +467,11 @@ bar satisfies number[]
       (as_expression (identifier) (predefined_type))
       (generic_type (type_identifier) (type_arguments (predefined_type)))))
   (expression_statement
-    (satisfies_expression (identifier) (array_type (predefined_type)))))
+    (satisfies_expression (identifier) (array_type (predefined_type))))
+  (expression_statement
+    (as_expression
+      (string
+        (string_fragment)))))
 
 =================================
 Ambient export function declarations

common/define-grammar.js

@@ -438,7 +438,7 @@ module.exports = function defineGrammar(dialect) {
       as_expression: $ => prec.left('binary', seq(
         $.expression,
         'as',
-        $._type
+        choice('const', $._type)
       )),
 
       satisfies_expression: $ => prec.left('binary', seq(