Add ViewportInfo::occluded and visible (#7948)

* Part of https://github.com/emilk/egui/issues/5112
* Part of https://github.com/emilk/egui/issues/5113
* Part of https://github.com/emilk/egui/issues/5136

Once we support calling `App::logic` when an app is occluded or
minimized, it is useful to know that it is, in fact, occluded or
minimized.

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

tests/test_background_logic/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "test_background_logic"
+version = "0.1.0"
+license = "MIT OR Apache-2.0"
+edition = "2024"
+rust-version = "1.92"
+publish = false
+
+[lints]
+workspace = true
+
+[dependencies]
+eframe = { workspace = true, features = ["default"] }
+env_logger = { workspace = true, features = ["auto-color", "humantime"] }