Add software rendering

[bluepilledgreat]

Ignore branch name, I forgot I was on it.
Closes #1273.

[bluepilledgreat]

Should software rendering become default?

[wilsontulus]

Should software rendering become default?

Not everyone has a good CPU for that, GPU rendering is more energy efficient, and what if you're on a CPU-heavy task like video transcoding?
(Unless if there's a specific program is designed for "cloud VM" usage which mostly lack GPU acceleration in the first place, but even then a toggle is necessary for GPU usage, plus more render efficiency.)

I also recommend to disable animations whenever possible if software rendering is used.
(About the rendering mode argument, I think -nogpu or -software is more accessible for accessing software rendering mode.)
Sad to see those old GPUs like AMD TeraScale 1 and Intel Gen4-Gen5 graphics aren't rendering WinUI elements properly.