New module header

Implements the new `module` header syntax as described in "module and package changes" [1]:

```
module [Request, Response, req]
```

The old syntax should still work fine, and is automatically upgraded to the new one
when running `roc format`.

[1] https://docs.google.com/document/d/1E_77fO-44BtoBtXoVeWyGh1xN2KRTWTu8q6i25RNNx0/edit

crates/compiler/test_syntax/fuzz/dict.txt

@@ -37,4 +37,4 @@
 ":="
 ":"
 "@"
-"->"
+"->"