Should we use prop:paren-shape instead of #%brackets

[SuzanneSoy]

Rationale:

• Being able to use (), [] and {} interchangeably for better readability in Racket is a nice feature.
• A few forms may want to make an explicit distinction, but these will be rare.
• For those forms, we could have some simple syntax/parse pattern expanders:
  • ~brackets
  • ~braces
  • and/or a more general ~paren-shape "⦃⦄"
  • See paren-shape-pattern-expanders, which implement some of this
• This was also the recommendation made to William G Hatch when he announced u-delim (use paren-shape instead of inserting new macros on the fly, so that the new delimiters can also work where the regular parentheses are expected).

I think #%dot should probably be kept, as it allows writing (a b . c d e)

See also: https://github.com/jeapostrophe/remix/issues/6