Add a way to tell Code to count specific characters as part of the word (preferably per language) when double clicking them

## Prerequisites
- [x] I have searched open and closed issues for duplicates.

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Ruby and Crystal allow `!` and `?` as part of variables and methods, so you can have a method like `File.exists? "~/abc"`. It would be useful if you could tell Code to count these characters as part of the word when double clicking them per language, so you could double click `exists?` and it would select the whole thing, rather than just `exists`.

...actually, it would probably be better to instead either use the language spec file for GtkSourceView to determine what to include in the double click select (if anything is even in the file for non-library variables and methods), or (possibly better) use language servers (#220) to determine that instead.

The latter would probably actually tell Code what you're double clicking (i.e. if what you're selecting is a variable/method/class/etc.) and so Code could use that to determine what to select (e.g. language server says what we double clicked is a method called `exists?`, so we should select the entirety of `exists?`), while the former may not even specify anything for non-library functions/methods/variables (i.e. your variables), so that's why the latter is probably better.