Lint against strings without wrapping <Text> (#3398)

* Add a rudimentary rule

* Get the rule passing

* Support special-casing text props

* More tests

eslint/index.js

@@ -0,0 +1,7 @@
+'use strict'
+
+module.exports = {
+  rules: {
+    'avoid-unwrapped-text': require('./avoid-unwrapped-text'),
+  },
+}