Migrate path handling to `camino` for UTF-8 valid paths

[imp]

Following the conversation in #6746 where migration to camino was mentioned as possible way address various issues with handling file paths on different platforms I wanted to experiment with that to get some feeling about the scale of the project. Turned out it was easier than I thought - see #6807.
The vast majority of the required changes is just a straightforward replacement.
So I wanted to share that to get discussion going.

• Is that a correct approach?
• Is there requirement for handling both UTF-8 and non-UTF-8 paths simultaneously?
• Any other relevant considerations?

[martinvonz]

The main reason we have not switched to camino is that we want to support non-utf-8. While relative paths within a repo are guaranteed to be utf-8, we have so far said that it should be allowed to store a clone in a directory that's not utf-8. So unless we decide that we no longer support that, I'm afraid there's not much we can use camino for right now.

[imp]

I see, thanks for pointing that out. In that case camino indeed won't help.
I am closing this ticket and associated PR.

[emilazy]

The main reason we have not switched to camino is that we want to support non-utf-8. While relative paths within a repo are guaranteed to be utf-8, we have so far said that it should be allowed to store a clone in a directory that's not utf-8. So unless we decide that we no longer support that, I'm afraid there's not much we can use camino for right now.

Why do we want that?

I think we get the Makefile problem even with repository paths, because of things like conditional configuration.

[yuja]

I don't know if people still use non-UTF-8 paths, but I don't think we should require that unless necessary.

I think we get the Makefile problem even with repository paths, because of things like conditional configuration.

I think it's less of a problem. Non-UTF-8 paths can't be specified by config file, so the user will have to move the repository if they really need conditional config.