Fix Jest cache for transform-react-version-pragma (#25712)

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## Summary
Jest caching wasn't working correctly for
`transform-react-version-pragma`. One condition for including
`transform-react-version-pragma` is that `process.env.REACT_VERSION` is
set, but it wasn't included in the cache key computation. Thus local
test runs would only run without `transform-react-version-pragma`, if
jest runs weren't using the `-reactVersion` flag and then added it.

Inlined the `scripts/jest/devtools/preprocessor.js` file, because it
makes it more obvious that `process.env.REACT_VERSION` is used in
`scripts/jest/preprocessor.js`

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Repro step:
- Clear jest cache
- node ./scripts/jest/jest-cli.js --build --project devtools
--release-channel=experimental --reactVersion 18.0
- node ./scripts/jest/jest-cli.js --build --project devtools
--release-channel=experimental

Before:
Jest cached the first run with `REACT_VERSION` set, so in the second run
`transform-react-version-pragma` is still there and runs only the
regression tests on old react versions.

After:
- The second run runs all tests and ignore `// @reactVersion` as
expected.

scripts/jest/preprocessor.js

@@ -7,7 +7,6 @@ const coffee = require('coffee-script');
 
 const tsPreprocessor = require('./typescript/preprocessor');
 const createCacheKeyFunction = require('fbjs-scripts/jest/createCacheKeyFunction');
-const {getDevToolsPlugins} = require('./devtools/preprocessor.js');
 
 const pathToBabel = path.join(
   require.resolve('@babel/core'),
@@ -26,6 +25,9 @@ const pathToTransformInfiniteLoops = require.resolve(
 const pathToTransformTestGatePragma = require.resolve(
   '../babel/transform-test-gate-pragma'
 );
+const pathToTransformReactVersionPragma = require.resolve(
+  '../babel/transform-react-version-pragma'
+);
 const pathToBabelrc = path.join(__dirname, '..', '..', 'babel.config.js');
 const pathToErrorCodes = require.resolve('../error-codes/codes.json');
 
@@ -83,8 +85,13 @@ module.exports = {
       const plugins = (isTestFile ? testOnlyPlugins : sourceOnlyPlugins).concat(
         babelOptions.plugins
       );
-      if (isTestFile && isInDevToolsPackages) {
-        plugins.push(...getDevToolsPlugins(filePath));
+      if (
+        isTestFile &&
+        isInDevToolsPackages &&
+        (process.env.REACT_VERSION ||
+          filePath.match(/\/transform-react-version-pragma-test/))
+      ) {
+        plugins.push(pathToTransformReactVersionPragma);
       }
       return babel.transform(
         src,
@@ -103,12 +110,19 @@ module.exports = {
     return src;
   },
 
-  getCacheKey: createCacheKeyFunction([
-    __filename,
-    pathToBabel,
-    pathToBabelrc,
-    pathToTransformInfiniteLoops,
-    pathToTransformTestGatePragma,
-    pathToErrorCodes,
-  ]),
+  getCacheKey: createCacheKeyFunction(
+    [
+      __filename,
+      pathToBabel,
+      pathToBabelrc,
+      pathToTransformInfiniteLoops,
+      pathToTransformTestGatePragma,
+      pathToTransformReactVersionPragma,
+      pathToErrorCodes,
+    ],
+    [
+      (process.env.REACT_VERSION != null).toString(),
+      (process.env.NODE_ENV === 'development').toString(),
+    ]
+  ),
 };