* Use dark-light on Mac and Windows
dark-light has a nasty problem on Linux: https://github.com/frewsxcv/rust-dark-light/issues/17
So we made dark-light opt-in in https://github.com/emilk/egui/pull/1437
This PR makes dark-light a default dependency again,
but only use it on Max and Windows.
This is controlled with the new NativeOptions::follow_system_theme.
If this isn't enabled, then NativeOptions::default_theme is used.
* Add eframe::WebOptions
* Remove integration name (it is always eframe)
* Remove egui_web crate
* Move egui_web/CHANGELOG.md into eframe/CHANGELOG.md
* Remove all mentions of egui_web
* Remove epi crate and absorb into eframe
* egui_glow: only use puffin on native
* Remove WASM doc from CI (we don't generate it anyways!)
* Remove eframe::epi and improve eframe docs