Add support for Window::set_icon() on MacOS

[GaiBrutman]

Describe the problem

When trying to change the app's window icon with window.set_icon(), I get the following error:
image `` extension not supported; please file a Tauri feature request (on 'png', 'jpg' and 'ico')

It looks like when compiled on MacOs, the extension option always panics:

tauri/core/tauri-runtime-wry/src/lib.rs

Lines 533 to 536 in 28dd9ad

	_ => panic!(
	"image `{}` extension not supported; please file a Tauri feature request",
	extension
	),

Describe the solution you'd like

Support for MacOS icon extensions needs to be added.

[GaiBrutman]

After looking into it, it seems like tau (as for 0.5.2) has no support for MacOS icons:
https://docs.rs/tao/0.5.2/tao/window/struct.Window.html#method.set_window_icon

[amrbashir]

indeed, setting an icon for a window on macos is not possible. however we can set the icon for the dock when we add dock management api. check #2358