Avoid unnecessarily importing isType from graphql.

To import `graphql` (and its internal `instanceOf` function) for the
first time with `process.env.NODE_ENV` safely polyfilled, PR #8347
selected a somewhat arbitrary export of the `graphql` package that uses
`instanceOf`, specifically the `isType` function exported by
`graphql/type/definition`.

As revealed by issue #8705, importing `isType` was a bad choice, since
it depends on a bunch of other code within the `graphql` package,
unnecessarily increasing minified+gzip bundle size by 3.4kB.

A better choice is the `Source` constructor, which is already imported
thanks to other necessary imports, and also imports/uses `instanceOf`.

src/utilities/globals/fix-graphql.ts

@@ -1,14 +1,14 @@
 // The ordering of these imports is important, because it ensures the temporary
 // process.env.NODE_ENV polyfill is defined globally (if necessary) before we
-// import { isType } from 'graphql'. The instanceOf function that we really care
+// import { Source } from 'graphql'. The instanceOf function that we really care
 // about (the one that uses process.env.NODE_ENV) is not exported from the
-// top-level graphql package, but isType uses instanceOf, and is exported.
+// top-level graphql package, but graphql/language/source uses instanceOf, and
+// has relatively few dependencies, so importing it here should not increase
+// bundle sizes as much as other options.
 import { remove } from 'ts-invariant/process';
-import { isType } from 'graphql';
+import { Source } from 'graphql';
 
 export function removeTemporaryGlobals() {
-  // Calling isType here just to make sure it won't be tree-shaken away,
-  // provided applyFixes is called elsewhere.
-  isType(null);
-  return remove();
+  // Using Source here here just to make sure it won't be tree-shaken away.
+  return typeof Source === "function" ? remove() : remove();
 }