react-css-modules: augment react's HTMLAttributes interface (#12184)

* augment react's HTMLAttributes interface with styleName

* move 'react-css-modules' declarations to top-level, turn on strictNullChecks

react-css-modules/tsconfig.json

@@ -3,7 +3,7 @@
         "module": "commonjs",
         "target": "es6",
         "noImplicitAny": true,
-        "strictNullChecks": false,
+        "strictNullChecks": true,
         "baseUrl": "../",
         "typeRoots": [
             "../"
@@ -15,4 +15,4 @@
     "files": [
         "index.d.ts"
     ]
-}
+}