Spaces allowed between `#` and argument?

```fstar
let wat # f = f+1
```
This works, and has an implicit `#f`. Should it?

The issue names no source file, parser entry point, or test. Reproduce the F* snippet, then trace how whitespace between `#` and `f` is parsed and find the relevant syntax tests; done means the intended behavior is documented by a regression test and the parser behavior matches that decision.

Written by the indexing model from the issue text.