Fix Js.String.match_ return type

Javscript String.prototype.match function can
return undefined values for optional capture groups
that are not found, which breaks the type annotations
since this is not added as a Js.nullable or an option,
it's not possible to deal with those.

Added an option type for array values.

Author: renatoalencar

jscomp/others/js_string.ml

@@ -274,7 +274,7 @@ external localeCompare : t -> float = "localeCompare" [@@bs.send.pipe: t]
 ]}
 
 *)
-external match_ : Js_re.t -> t array option = "match" [@@bs.send.pipe: t] [@@bs.return {null_to_opt}]
+external match_ : Js_re.t -> t option array option = "match" [@@bs.send.pipe: t] [@@bs.return {null_to_opt}]
 
 (** [normalize str] returns the normalized Unicode string using Normalization Form Canonical (NFC) Composition.
 

jscomp/others/js_string2.ml

@@ -273,7 +273,7 @@ external localeCompare : t -> t -> float = "localeCompare" [@@bs.send]
 ]}
 
 *)
-external match_ : t -> Js_re.t -> t array option = "match" [@@bs.send] [@@bs.return {null_to_opt}]
+external match_ : t -> Js_re.t -> t option array option = "match" [@@bs.send] [@@bs.return {null_to_opt}]
 
 (** [normalize str] returns the normalized Unicode string using Normalization Form Canonical (NFC) Composition.
 

jscomp/test/js_string_test.ml

@@ -84,11 +84,14 @@ let suites = Mt.[
     );
 
     "match", (fun _ ->
-      Eq(Some [| "na"; "na" |], "banana" |. Js.String2.match_ [%re "/na+/g"])
+      Eq(Some [| Some "na"; Some "na" |], "banana" |. Js.String2.match_ [%re "/na+/g"])
     );
     "match - no match", (fun _ ->
       Eq(None, "banana" |. Js.String2.match_ [%re "/nanana+/g"])
     );
+    "match - not found capture groups", (fun _ ->
+      Eq(Some [| Some "hello "; None |], "hello word" |. Js.String2.match_ [%re "/hello (world)?/"] |. Belt.Option.map Js.Array.copy )
+    );
 
     (* es2015 *)
     "normalize", (fun _ ->