Improve auto-pairing in code editor

[PalumboN]

We refer to auto-pairing to the way of automatically close brackets and quotes (and other "smart characters") when you open them.

In the next gif, we can see how both parenthesis are written when I just input (, and removed when I remove it. But there are some border cases where this is not working well (for example, for removing [ ]).

Current problems

• The logic to make the pairing of the "smart characters" on smart remove is not accurate (look the methods on CompletionEngine class with smartBackspace*, for example smartNeedExtraRemovePairedIn:for:opposite:at: ): it is looking on all the text, including comments, for example, what it's not correct.

• Now the smart remove only works if the characters are adjacent. For example, in the gif above, the [ ] are inserted with n space in the middle. So, when I remove the open [, the close one ] is not removed.

[AlexisCnockaert]

Hello @PalumboN and @Gabriel-Darbord, I fixed this issue and ready to make a PR but I saw too late that it was for a project linked to GSoC 2025, do I keep my work for me or not ? :)

[Gabriel-Darbord]

@AlexisCnockaert This issue is related to a GSoC project, but it is not exclusive to GSoC. If you have a fix, please do a PR :)