Typecheck much more of the config loading process (#5642)

* Add type declarations for micromatch.

* Enable Flowtype on all config loading.

* Remove unneeded comments.

packages/babel-plugin-transform-react-jsx/test/fixtures/react/honor-custom-jsx-comment-if-jsx-pragma-option-set/options.json

@@ -1,3 +1,5 @@
 {
-  "plugins": [["transform-react-jsx", "foo.bar"]]
+  "plugins": [
+    ["transform-react-jsx", {"pragma": "foo.bar"}]
+  ]
 }