[Flight] Support FormData from Server to Client (#28754)

We currently support FormData for Replies mainly for Form Actions. This
supports it in the other direction too which lets you return it from an
action as the response. Mainly for parity.

We don't really recommend that you just pass the original form data back
because the action is supposed to be able to clear fields and such but
you could potentially at least use this as the format and could clear
some fields.

We could potentially optimize this with a temporary reference if the
same object was passed to a reply in case you use it as a round trip to
avoid serializing it back again. That way the action has the ability to
override it to clear fields but if it doesn't you get back the same as
you sent.

#28755 adds support for Blobs when the `enableBinaryFlight` is enabled
which allows them to be used inside FormData too.

DiffTrain build for [2acfb7b](2acfb7b)

compiled/facebook-www/REVISION

@@ -1 +1 @@
-d1547defe34cee6326a61059148afc83228d8ecf
+2acfb7b60922bdc8376dd144ca7bc532df78254b

compiled/facebook-www/ReactFlightDOMClient-dev.modern.js

@@ -839,6 +839,21 @@ if (__DEV__) {
             return undefined;
           }
 
+          case "K": {
+            // FormData
+            var _id7 = parseInt(value.slice(2), 16);
+
+            var _data3 = getOutlinedModel(response, _id7);
+
+            var formData = new FormData();
+
+            for (var i = 0; i < _data3.length; i++) {
+              formData.append(_data3[i][0], _data3[i][1]);
+            }
+
+            return formData;
+          }
+
           case "I": {
             // $Infinity
             return Infinity;
@@ -891,9 +906,9 @@ if (__DEV__) {
 
           default: {
             // We assume that anything else is a reference ID.
-            var _id7 = parseInt(value.slice(1), 16);
+            var _id8 = parseInt(value.slice(1), 16);
 
-            var _chunk2 = getChunk(response, _id7);
+            var _chunk2 = getChunk(response, _id8);
 
             switch (_chunk2.status) {
               case RESOLVED_MODEL:

compiled/facebook-www/ReactFlightDOMClient-prod.modern.js

@@ -296,6 +296,13 @@ function parseModelString(response, parentObject, key, value) {
         );
       case "B":
         return;
+      case "K":
+        parentObject = parseInt(value.slice(2), 16);
+        response = getOutlinedModel(response, parentObject);
+        parentObject = new FormData();
+        for (key = 0; key < response.length; key++)
+          parentObject.append(response[key][0], response[key][1]);
+        return parentObject;
       case "I":
         return Infinity;
       case "-":

compiled/facebook-www/ReactFlightDOMServer-dev.modern.js

@@ -2032,6 +2032,12 @@ if (__DEV__) {
       return "$Q" + id.toString(16);
     }
 
+    function serializeFormData(request, formData) {
+      var entries = Array.from(formData.entries());
+      var id = outlineModel(request, entries);
+      return "$K" + id.toString(16);
+    }
+
     function serializeSet(request, set) {
       var entries = Array.from(set);
 
@@ -2338,6 +2344,10 @@ if (__DEV__) {
 
         if (value instanceof Set) {
           return serializeSet(request, value);
+        } // TODO: FormData is not available in old Node. Remove the typeof later.
+
+        if (typeof FormData === "function" && value instanceof FormData) {
+          return serializeFormData(request, value);
         }
 
         var iteratorFn = getIteratorFn(value);
@@ -2730,6 +2740,10 @@ if (__DEV__) {
 
         if (value instanceof Set) {
           return serializeSet(request, value);
+        } // TODO: FormData is not available in old Node. Remove the typeof later.
+
+        if (typeof FormData === "function" && value instanceof FormData) {
+          return serializeFormData(request, value);
         }
 
         var iteratorFn = getIteratorFn(value);

compiled/facebook-www/ReactFlightDOMServer-prod.modern.js

@@ -862,6 +862,11 @@ function renderModelDestructive(
               parentPropertyName.set(parent, -1));
       return "$W" + outlineModel(request, value).toString(16);
     }
+    if ("function" === typeof FormData && value instanceof FormData)
+      return (
+        (value = Array.from(value.entries())),
+        "$K" + outlineModel(request, value).toString(16)
+      );
     null === value || "object" !== typeof value
       ? (parent = null)
       : ((parent =