Js_bigint adding operations

Author: mununki

jscomp/others/js_bigint.res

@@ -1,3 +1,11 @@
 /*** JavaScript BigInt API */
 
-type t
+type t = bigint
+
+external \"~-": t => t = "%negbigint"
+external \"~+": t => t = "%identity"
+external \"+": (t, t) => t = "%addbigint"
+external \"-": (t, t) => t = "%subbigint"
+external \"*": (t, t) => t = "%mulbigint"
+external \"/": (t, t) => t = "%divbigint"
+external mod: (t, t) => t = "%modbigint"