Move babel config back to it's own file

It's need for jest to work properly.

babel.config.js

@@ -0,0 +1,6 @@
+module.exports = function (api) {
+  const defaultConfigFunc = require("shakapacker/package/babel/preset.js");
+  const resultConfig = defaultConfigFunc(api);
+
+  return resultConfig;
+};

jest.config.js

@@ -179,7 +179,7 @@ module.exports = {
   // transform: { "\\.[jt]sx?$": "babel-jest" },
 
   // An array of regexp pattern strings that are matched against all source file paths, matched files will skip transformation
-  transformIgnorePatterns: ["/node_modules/(?!(stimulus.+)/)"],
+  transformIgnorePatterns: ["/node_modules/(?!stimulus)/"],
 
   // An array of regexp pattern strings that are matched against all modules before the module loader will automatically return a mock for them
   // unmockedModulePathPatterns: undefined,

package.json

@@ -60,11 +60,6 @@
     "webpack-merge": "^5.8.0",
     "webpack-sources": "^3.3.3"
   },
-  "babel": {
-    "presets": [
-      "./node_modules/shakapacker/package/babel/preset.js"
-    ]
-  },
   "browserslist": [
     "defaults",
     "not IE 11"