Fix handling of escaped chars in strings

corpus/literals.txt

@@ -306,3 +306,16 @@ a+=(foo "bar" $(baz))
       (word)
       (string)
       (command_substitution (command (command_name (word)))))))
+
+==============================
+Escaped characters in strings
+==============================
+
+echo -ne "\033k$1\033\\" > /dev/stderr
+
+---
+
+(program
+  (redirected_statement
+    (command (command_name (word)) (word) (string (simple_expansion (variable_name))))
+    (file_redirect (word))))

grammar.js

@@ -425,7 +425,7 @@ module.exports = grammar({
       '"'
     ),
 
-    _string_content: $ => token(prec(-1, /([^"`$]|\\.)+/)),
+    _string_content: $ => token(prec(-1, /([^"`$\\]|\\(.|\n))+/)),
 
     array: $ => seq(
       '(',