Detect classes inside Elixir charlist, word list, and string sigils

[thecrypticace]

Fixes #18431

The ~W(…) syntax in Elixir is a sigil. It's basically another way to write strings, arrays of strings, etc… The syntax lets you use a handful of surrounding brackets like ~W(…), ~W[…], ~W{…}, ~W"…", etc… to let you write lists without necessarily having to escape characters.

In v3 our extractor was able to pick these up but in v4 Oxide does not. I've added a preprocessor for Elixir files so we can modify the code before our main extractor sees it.

Now things like this: ~W(text-white bg-gray-600) will get turned into ~W text-white bg-gray-600 which can easily be processed by our extractor.

The sigils we support are:

• ~s / ~S (strings)
• ~w / ~W (word lists)
• ~c / ~C (charlists)

We're specifically detecting the use of (…), […], and {…} as using quotes already works today.

[thecrypticace]

@RobinMalfait if you could take a peek at this at some point. I think I did it right 😅

[RobinMalfait]

Apart from these 2 suggestions, looks good!

The Elixir::test already makes sure that we keep the same length so that's already covered for us.