Move away from std::Path in bevy_assets

[alice-i-cecile]

Future PR: Cart has previously expressed a desire to move away from std::path::Path, as AssetPath shouldn't support platform-specific functionality like Windows prefixes or different path separators. AssetPath should always use str instead of Path, but that will requiring providing our own implementations for common Path operations (components, file_name, etc.).

Originally posted by @bushrat011899 in #19070 (comment)

[lielfr]

Hi,
I'd like to work on this if possible.
Just to make sure I understand the intentions clearly:

• The scope is only the bevy_asset crate, and more specifically the AssetPath struct
• The path separator should aways be a forward slash, e.g. a/b/c/d

Thanks

[alice-i-cecile]

That's my understanding on both counts :)