Normalize command-line argument paths

[catboxanon]

Description

This aims to fix an issue on Windows where some functions will misbehave if forward slashes are provided rather than double backslashes. An example of this is the current tree generation procedure implemented in https://github.com/AUTOMATIC1111/stable-diffusion-webui/pull/14588, which produces no tree if a path with forward slashes X:/like/this is provided via the cmd line arg rather than backslashes X:\\like\\this.

This would partially resolve the issue being experienced here: https://github.com/lllyasviel/stable-diffusion-webui-forge/issues/121

Checklist:

• [x] I have read contributing wiki page
• [x] I have performed a self-review of my own code
• [x] My code follows the style guidelines
• [x] My code passes tests