Combine createElement and JSX modules (#28320)

Depends on:

- #28317

---

There's a ton of overlap between the createElement implementation and
the JSX implementation, so I combined them into a single module.

In the actual build output, the shared code between JSX and
createElement will get duplicated anyway, because react/jsx-runtime and
react (where createElement lives) are separate, flat build artifacts.

So this is more about code organization — with a few key exceptions, the
implementations of createElement and jsx are highly coupled.

DiffTrain build for [5fb2c93](5fb2c93)

compiled/facebook-www/JSXDEVRuntime-dev.classic.js

@@ -252,6 +252,8 @@ if (__DEV__) {
     // $FlowFixMe[method-unbinding]
     var hasOwnProperty = Object.prototype.hasOwnProperty;
 
+    var assign = Object.assign;
+
     /*
      * The `'' + value` pattern (used in perf-sensitive code) throws for Symbol
      * and Temporal.* types. See https://github.com/facebook/react/pull/22064.
@@ -375,8 +377,6 @@ if (__DEV__) {
       return isArrayImpl(a);
     }
 
-    var assign = Object.assign;
-
     // Helpers to patch console.logs to avoid logging during side-effect free
     // replaying on render function. This currently only patches the object
     // lazily which won't cover if the log function was extracted eagerly.
@@ -1389,13 +1389,11 @@ if (__DEV__) {
      */
 
     function isValidElement(object) {
-      {
-        return (
-          typeof object === "object" &&
-          object !== null &&
-          object.$$typeof === REACT_ELEMENT_TYPE
-        );
-      }
+      return (
+        typeof object === "object" &&
+        object !== null &&
+        object.$$typeof === REACT_ELEMENT_TYPE
+      );
     }
     var ownerHasKeyUseWarning = {};
     /**

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

@@ -252,6 +252,8 @@ if (__DEV__) {
     // $FlowFixMe[method-unbinding]
     var hasOwnProperty = Object.prototype.hasOwnProperty;
 
+    var assign = Object.assign;
+
     /*
      * The `'' + value` pattern (used in perf-sensitive code) throws for Symbol
      * and Temporal.* types. See https://github.com/facebook/react/pull/22064.
@@ -375,8 +377,6 @@ if (__DEV__) {
       return isArrayImpl(a);
     }
 
-    var assign = Object.assign;
-
     // Helpers to patch console.logs to avoid logging during side-effect free
     // replaying on render function. This currently only patches the object
     // lazily which won't cover if the log function was extracted eagerly.
@@ -1389,13 +1389,11 @@ if (__DEV__) {
      */
 
     function isValidElement(object) {
-      {
-        return (
-          typeof object === "object" &&
-          object !== null &&
-          object.$$typeof === REACT_ELEMENT_TYPE
-        );
-      }
+      return (
+        typeof object === "object" &&
+        object !== null &&
+        object.$$typeof === REACT_ELEMENT_TYPE
+      );
     }
     var ownerHasKeyUseWarning = {};
     /**

compiled/facebook-www/REVISION

@@ -1 +1 @@
-ec160f32c28ccab798c73ecccbb36ce121e1640e
+5fb2c93f3924ba980444da5698f60651b5ef0689