[flow][test] Add additional test for declare global {...} without e…

…xplicit react import

Summary:
The added test helps to ensure that the globals can still be correctly used even when react is not imported. It helps to test the interaction between the declare global feature and the implicit inclusion of react import in file_sig.

Changelog: [internal]

Reviewed By: panagosg7

Differential Revision: D69133647

fbshipit-source-id: c13a169e64e14ce1bc35e8411413d372a231e88a

tests/declare_global_in_react_module/declare_global_in_react_module.exp

@@ -85,5 +85,20 @@ References:
             ^^ [2]
 
 
+Error ----------------------------------------------------------------------------- test_no_explicit_react_import.js:1:1
 
-Found 7 errors
+Cannot cast empty string to `MyReact` because string [1] is incompatible with string literal `react` [2].
+[incompatible-cast]
+
+   test_no_explicit_react_import.js:1:1
+   1| '' as ReactTypes.MyReact; // error: '' ~> 'react'
+      ^^ [1]
+
+References:
+   test_no_explicit_react_import.js:1:7
+   1| '' as ReactTypes.MyReact; // error: '' ~> 'react'
+            ^^^^^^^^^^^^^^^^^^ [2]
+
+
+
+Found 8 errors

tests/declare_global_in_react_module/test_no_explicit_react_import.js

@@ -0,0 +1 @@
+'' as ReactTypes.MyReact; // error: '' ~> 'react'