Allow Setting Window Class (WM_CLASS) on Linux

[tareqimbasher]

Is your feature request related to a problem? Please describe.
The WebviewWindowBuilder in Tauri allows setting the WM_CLASS using the window_classname function. But this only works for Windows. Using this function on Linux has no effect, as documented on the function itself (link).

Describe the solution you'd like
I'm requesting the ability to set WM_CLASS on Linux, and macOS if possible.

Describe alternatives you've considered
There aren't alot of great alternative solutions to this besides "fixing" the window class name post-creation using tools like xdotool, and that only works on Xorg, not Wayland.