Unified Search Redesign

Supersedes #59766 Unified Search is incredibly useful and its performance is technologically very impressive. Unfortunately, its UI has not received nearly as much love as its implementations. Making it more visible, as mocked-up in #59888 means it's the right time to also improve its usability. Loading The main advantage of unified search is being able to find anything in Nextcloud fast. This is undermined by how results are loaded. Before all results have loaded, the UI is plagued by frequent flashing, which slows down the process of finding a result. I will describe an algorithm in an imperative manner that aims to fix this problem and still return results quickly without disrupting a familiar order. --- Results are loaded per-category, as they are now. Categories can be in one of the following four states: ⬜️ Loading 🟩 Loaded 🟨 Blocked 🟥 Failed --- All of them start out as ⬜️ loading, in their preferred order. We also start a 1500ms (TBD) ⏳ timer. ⏳ 0ms ⬜️ Apps ⬜️…