[Textual] Parse constants with parens

[effectfully]

This makes the parse recognize constants with extra parens in them as requested in #7383.

I don't feel like we want to make any of those extra parens mandatory, but there's no harm in being lenient and parsing them.

[carloskiki]

I'm not sure this is better. I would rather have an inconsistent syntax with a single way of doing things, than a partially consistent syntax with non-canonical ways of doing things.

[effectfully]

I don't care either way.

My justification is that for constants we mostly reuse Haskell syntax and there parsing of redundant parens is mostly supported:

>>> read "[(True),(False)]" :: [Bool]
[True,False]
>>> read "[((1,2)),((3,4))]" :: [(Int, Int)]
[(1,2),(3,4)]
>>> read "[((1,2),(3,4))]" :: [((Int, Int), (Int, Int))]
[((1,2),(3,4))]

If any of the reviewers don't like this PR, feel free to close it.

[zliu41]

I think the expectParens parameter is useless now?

[effectfully]

Nope, we still can't allow (con data I 42), it has to be (con data (I 42)).
While (con (list data) [I 42]) is fine.
So the distinction still exists.

[kwxm]

I'm not too sure about the arbitrarily nested parentheses.

Also, we should probably have some conformance tests here.

[kwxm]

This now accepts

(con (list data) [ (((((((((((I 5))))))))))), B #FF ])

and

(con unit (((((((((((((((((((()))))))))))))))))))))

Do we really want that?

[kwxm]

Also, the prettyprinter still prints list elements without parentheses. I suppose we have to choose one way or the other, so that seems fine.