Remove not_nil! from Regex::MatchData docs

[devnote-dev]

The documentation for Regex uses a lot of not_nil! in the code examples, and is one of only 4 pages to do this, but it should not be like this. It is generally recommended to not use this method where possible (or unless absolutely necessary, IMO) and the Regex docs should reflect that.

Most (if not all) of the examples are to do with the String#match method which is nilable, so I have created #13119 to address that, but another solution could be to recommend the conditional statement check syntax. For example, take Regex::MatchData#[] which has the following code example:

"Crystal".match(/r(?<ok>ys)/).not_nil!["ok"] # => "ys"
"Crystal".match(/r(?<ok>ys)/).not_nil!["ng"] # raises KeyError

This could easily be changed to:

if matches = "Crystal".match(/r(?<ok>ys)/)
  matches["ok"] # => "ys"
  matches["ng"] # raises KeyError
end

I believe that this is much clearer than the existing example and it effectively avoids using not_nil! thanks to the conditional logic.

WDYT?

[straight-shoota]

If #match! gets implemented, I think that would be the most concise way to get rid of .not_nil!.
So let's wait for the resolution of #13119

[stufro]

I was looking at picking this one up but now #13285 has changed all the documentation for Regex::MatchData

Can this issue be closed now?