Convert Legacy UI to PCUI

[kpal81xd]

There still exists a lot of references to custom Legacy UI elements in the codebase. These should be migrated only use PCUI

[willeastcott]

I've gradually been doing this migration over an extended period. The Code Editor is now 100% PCUI. The main Editor still has a lot of legacy UI usage. By yeah, it would be good to gradually eliminate the legacy stuff. PCUI is so awesome now, powering several great apps! ❤️

[Maksims]

That tooltip is snappy, clean and precise, spawning where it should be.
There should be a decent alternative to migrate from it, as the current alternative has degraded UX and cleanness.