feature: Allow serving compressed SVG images (rebased)

[flavorjones]

Motivation / Background

This adds image/svg+xml to the compressible content types of ActionDispatch::Static

(This is a rebased re-submission of #42407 by @ledermann which was approved by @zzak in 2021)

Detail

Original description:

This adds image/svg+xml to the compressible content types of ActionDispatch::Static so GZIP or Brotli can be used.

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug or add a feature.
• CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature. Minor bug fixes and documentation changes should not be included.

[tvdeyen]

@byroot could Rails core team consider to release this in the next patch level of 7.1 please 🙏🏻?

Since the footprint is very small, but the impact on apps huge and it already has been approved in 2021 (but never merged) it would be great to not have to wait until 7.2 (or 8) comes out.

/cc @dhh @rafaelfranca

[skipkayhil]

could Rails core team consider to release this in the next patch level of 7.1 please 🙏🏻?

(Not on the Core team, so take my opinion with a grain of salt)

I don't see a reason to backport a feature like this when you can add this to your app today:

config.public_file_server.enabled = false # disable the default Static middleware configuration
config.middleware.insert_after ::Rack::Sendfile, ActionDispatch::Static, config.paths["public"].first, index: config.public_file_server.index_name, headers: config.public_file_server.headers || {}, compressible_content_types: /\A(?:text\/|application\/javascript|image\/svg\+xml)/

[tvdeyen]

Nice. Will try. Thanks