Create Pagefind ranking playground

[bglw]

Ranking is a bit of an opaque box at the moment, and making changes to the algorithm can be hard without good confidence in the end result.

The first step to being able to do this is to create some kind of ranking playground for Pagefind. The exact format of this is up for discussion, but at a minimum it should allow searching an example (or ideally user-supplied) index, while changing the ranking parameters live to see how they affect the results. It should also provide deeper debug information on the scoring for each result.

A while ago I set up a Rust playground containing the core essentials of the ranking, which can be seen here: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=be766fc0ffe54b9981587d2a8fe6dafe

This playground allows us to change the code itself, which is useful, though it isn't a great space to visualize searches of a larger real-world index.