Implement variable sized bit array pattern matching on JavaScript

[GearsDatapacks]

This PR implements the ability to pattern match on dynamically sized bit array segments on JavaScript.

[lpil]

Wonderful, thank you!!!

I've left a bunch of little nit-pick notes inline, and it would be fab to remove all the clones.

I couldn't see any tests that involve extra, and there's no integration tests to check that that the runtime behaviour is correct. Here's an example bit array PR's integration tests: https://github.com/gleam-lang/gleam/pull/3946/files#diff-42aefabdf30f6176dcac76f43f95e6af038909579ce30683824c7fc2d98c3db9

Thanks again!

[lpil]

Wonderful work, as always! Thank you!!

[GearsDatapacks]

What should I do about the linter errors? Should I use the shorthand *= and /= or should I disable that lint?

[GearsDatapacks]

Ah, looks like tests are failing due to #3253. I guess I just have to work around that for now?

[lpil]

Reworking the test to avoid that bug could be good

[GearsDatapacks]

Oops, forgot 928 doesn't fit within 8 bits

[GearsDatapacks]

Ok sorry this has been a bit of a mess. Should be ready to merge now

[GearsDatapacks]

I've decided to follow your comment and replace the usage of Document in variables with EcoString. It makes it a bit easier to work with and removes most of the cloning. (The only cloning now is of EcoStrings, which is cheap)

[lpil]

Beautiful!! Thank you!