Enable debugging info for JSX elements in dev builds and tests

Enable the "development" [1] option for the `@babel/preset-react` preset
to enable more helpful warnings/errors from Preact in development
builds.

Note that the configuration added here _replaces_ rather than _augments_
the `@babel/preset-react` config for other builds, so other keys like
"createElement" also need to be specified in both places.

See https://babeljs.io/docs/en/babel-preset-react#development.

.babelrc

@@ -13,5 +13,15 @@
     "angularjs-annotate",
     "transform-async-to-promises"
   ],
-  "ignore": ["**/vendor/*"]
+  "ignore": ["**/vendor/*"],
+  "env": {
+    "development": {
+      "presets": [
+        ["@babel/preset-react", {
+          "development": true,
+          "pragma": "createElement"
+        }]
+      ]
+    }
+  }
 }