Custom window frames for Windows and Linux

[emilk]

Currently the viewer frame on Windows and Linux have an ugly platform-specific header with a title, close buttons, and a minimize button.

We should just replace those with our own window frame, like in https://github.com/emilk/egui/tree/master/examples/custom_window_frame

TODO:

• Fix window resizing UI on Wayland and Xorg
• Fix lower right corner (paint_time_ranges_gaps). Maybe turn off rounding?
• Test on Windows
• Custom icons for close/maximize/minimize
• I think we need to center the panel buttons?

---

What Rerun currently looks like on Gnome/xorg:

If you enable CUSTOM_WINDOW_DECORATIONS on main:

[emilk]

There are a bunch of open issues with custom window frames in eframe: https://github.com/emilk/egui/issues?q=is%3Aissue+is%3Aopen+custom_window_frame

[teh-cmc]

Custom decorations working fine on Linux/Wayland/Sway.

 /// If true, we fill the entire window, except for the close/maximize/minimize buttons in the top-left.
 /// See <https://github.com/emilk/egui/pull/2049>
-pub const FULLSIZE_CONTENT: bool = cfg!(target_os = "macos");
+pub const FULLSIZE_CONTENT: bool = true;
 
 /// If true, we hide the native window decoration
 /// (the top bar with app title, close button etc),
 /// and instead paint our own close/maximize/minimize buttons.
-pub const CUSTOM_WINDOW_DECORATIONS: bool = false; // !FULLSIZE_CONTENT; // TODO(emilk): https://github.com/rerun-io/rerun/issues/1063
+pub const CUSTOM_WINDOW_DECORATIONS: bool = true; // !FULLSIZE_CONTENT; // TODO(emilk): https://github.com/rerun-io/rerun/issues/1063

Close button works as expected -- others don't but that's expected on my setup.

[Wumpf]

Using the same diff on Windows 11:

Minimize/maximize/close work.

Issues:

• minimize/maximize/close look unusually small for windows, close button doesn't get red on hover like most other applications (btw. some fade red in some don't... I miss the good old days of native ui everywhere :( )
• window corners are not transparent/cutout
• resize at window border doesn't work