Extract a base component for blacklight

[barmintor]

Backports #2679 to 7.x

[barmintor]

Since we've made a decision on main regarding base components, I've decided to take the more conservative approach to overrides and substitute in a ViewComponent::Compiler subclass for descendants of Blacklight::Component in this PR.

This allows simple overrides of component templates that exist in the engine by placing them in the same place in the installing application. If a file in the installing application doesn't have a same-named analog in the engine, it won't be recognized - this has an impact on translation sidecars if the installing app is more expansive than the engine in language scope. But the Compiler interface is more stable, and if ViewComponent commits to an interface for sidecar files we can revisit without disrupting existing apps.

[jcoyne]

Please add documentation around what this is doing and why.

[barmintor]

Documentary comments added.