Move Liquid filters into a separate gem

[jaredcwhite]

We have a monorepo with multiple gems now, but something we haven't done too much of yet is identify pieces of the core gem we can extract into a separate gem.

Filters seem to be a great place to start (and any utility methods they rely on). A few filters are very much tied to internal Bridgetown data structures, but many of them are pretty generic and can be used in any context. With a separate gem, other projects could simply require bridgetown-filters and use them without having to require any other gem in the project. For instance, Rails apps using view_component_liquid could easily make use of all these filters.

This would also be a good opportunity to identify new filters which might be useful to add. Jekyll 4.1 just added new find-* filters which seem quite helpful. (see jekyll/jekyll#8171) I'd love to see a bunch more related to ActiveSupport as well. AS is a treasure-trove of cool enhancements to core Ruby data types and the more we can bring that goodness to Liquid templates the better IMHO.

[jaredcwhite]

Forgot to mention this should also include reviewing the latest state of built-in Liquid filters and any other major open-source filter libraries out there to see if we can actually remove some of our own code in the process. (Less code FTW! 😆)

[jaredcwhite]

This might morph in scope a bit now that we have Ruby-based templates and helpers…we should identify which filters are useful as helpers and keep them conceptually a bit separate from filters which are only useful in a Liquid template. That way we can include only the helper-appropriate methods.

[jaredcwhite]

I think this is now feeling like too much complexity for not enough real-world gain, so closing. Can always reopen in the future.