Change definition of BNF production `funlhs` to allow additional parentheses

GHC deviates from the report in how it implements the `funlhs` production in the grammar. This is documented here: https://downloads.haskell.org/ghc/latest/docs/users_guide/bugs.html#lexical-syntax

> GHC allows redundant parantheses around the function name in the funlhs part of declarations. That is GHC will succeed in parsing a declaration like ((f)) x = for any number of parantheses around f.

Start with the report's BNF definition of the `funlhs` production and compare it with the linked GHC lexical-syntax documentation. Update the production so declarations such as `((f)) x = ` are accepted with any number of redundant parentheses, and verify that the report matches the documented behavior.

Written by the indexing model from the issue text.