[flow][libdef] Update typing for React.Context to align with React …

…19 changes

Summary:
In React 19, created react context `MyContext` can be used in places that expects `MyContext.Provider`. This diff updates the libdef to support that.

This is implemented as an intersection type behind an opaque type.

Close #9245

Changelog: [lib] Type for `React.Context` has been updated to support [React 19's context as provider model](https://react.dev/blog/2024/12/05/react-19#context-as-a-provider). Given this change, you might need additional annotations on exports. e.g.

```
const Context: React.Context<Foo> = React.createContext(...);

export const MyProvider = Context.Provider;
//             ^ annotation now required
```

Reviewed By: alexmckenley

Differential Revision: D67993213

fbshipit-source-id: cb717f4449a39d8614143f84e11990704462b6f4

lib/react.js

@@ -203,7 +203,11 @@ declare type React$RefSetter<-T> =
  * The type of a React Context.  React Contexts are created by calling
  * createContext() with a default value.
  */
-declare type React$Context<T> = {
+declare opaque type React$Context<T>: React$ComponentType<{
+  +value: T,
+  +children?: React$Node,
+  ...
+}> & {
   Provider: React$ComponentType<{
     +value: T,
     +children?: React$Node,

tests/badly_positioned_react/badly_positioned_react.exp

@@ -14,8 +14,8 @@ References:
    test.js:21:29
     21| const Foo1 = create(create1<{||}>(Foo));
                                     ^^^^ [2]
-   <BUILTINS>/react.js:349:38
-   349|   declare export type ComponentType<-P> = React$ComponentType<P>;
+   <BUILTINS>/react.js:353:38
+   353|   declare export type ComponentType<-P> = React$ComponentType<P>;
                                              ^ [3]
 
 

tests/component_syntax_unsupported/component_syntax_unsupported.exp

@@ -17,11 +17,11 @@ Cannot cast `3` to `React.FragmentType` because number [1] is incompatible with
          ^ [1]
 
 References:
-   <BUILTINS>/react.js:748:5
+   <BUILTINS>/react.js:752:5
             v------------------------------------------------------
-   748|     declare component Fragment<Renders: React$Node = void>(
-   749|       children?: Renders,
-   750|     ) renders Renders;
+   752|     declare component Fragment<Renders: React$Node = void>(
+   753|       children?: Renders,
+   754|     ) renders Renders;
             -----------------^ [2]
 
 

tests/component_type/component_type.exp

@@ -321,8 +321,8 @@ References:
    component_to_component.js:26:37
     26|   x: component(ref: React.RefSetter<Component>, ...{...}),
                                             ^^^^^^^^^ [2]
-   <BUILTINS>/react.js:365:34
-   365|   declare export type RefSetter<-T> = React$RefSetter<T>;
+   <BUILTINS>/react.js:369:34
+   369|   declare export type RefSetter<-T> = React$RefSetter<T>;
                                          ^ [3]
 
 
@@ -426,8 +426,8 @@ Cannot create `C` element because in property `ref`: [incompatible-type]
                                                 ^^^^^^
 
 References:
-   <BUILTINS>/react.js:698:8
-   698|     ): React$RefObject<T | null>;
+   <BUILTINS>/react.js:702:8
+   702|     ): React$RefObject<T | null>;
                ^^^^^^^^^^^^^^^^^^^^^^^^^ [1]
    <BUILTINS>/react.js:197:6
    197|   | ((T | null) => mixed)
@@ -575,8 +575,8 @@ References:
    <BUILTINS>/core.js:2060:19
    2060| declare class Set<T> extends $ReadOnlySet<T> {
                            ^ [3]
-   <BUILTINS>/react.js:235:19
-    235|   type RefSetter<-T> = React$RefSetter<T>;
+   <BUILTINS>/react.js:239:19
+    239|   type RefSetter<-T> = React$RefSetter<T>;
                            ^ [4]
 
 
@@ -991,8 +991,8 @@ References:
    <BUILTINS>/core.js:2060:19
    2060| declare class Set<T> extends $ReadOnlySet<T> {
                            ^ [3]
-   <BUILTINS>/react.js:235:19
-    235|   type RefSetter<-T> = React$RefSetter<T>;
+   <BUILTINS>/react.js:239:19
+    239|   type RefSetter<-T> = React$RefSetter<T>;
                            ^ [4]
 
 

tests/new_generics/new_generics.exp

@@ -1031,8 +1031,8 @@ References:
    react.js:13:28
     13|   a as React.ComponentType<{a: number}>; // nope, contravariance
                                    ^^^^^^^^^^^ [2]
-   <BUILTINS>/react.js:349:38
-   349|   declare export type ComponentType<-P> = React$ComponentType<P>;
+   <BUILTINS>/react.js:353:38
+   353|   declare export type ComponentType<-P> = React$ComponentType<P>;
                                              ^ [3]