Upgrade to Blacklight 8.4.0

[jcoyne]

closes #1282

[dnoneill]

Approved, not sure if we want to point the css on npm and not build from gem https://github.com/sul-dlss/earthworks/pull/1229/files#r1735246549. Granted vt-arclight does this and it might not matter in the gem is stable?

[thatbudakguy]

@dnoneill can you clarify what you meant here? Don't we always have to build the styles from npm?

[dnoneill]

@thatbudakguy See comment here: https://github.com/sul-dlss/earthworks/pull/1229/files#r1735246549. This PR doesn't remove the build-css script. We used to pull directly from npm not the gem.

[thatbudakguy]

Ah, thanks for explaining. Honestly, pulling from the gem makes it easier to get updates more quickly, and since few other people are working on the 5.x branch, it might be beneficial for the time being...