Initial fs implementation for UEFI

[Ayush1325]

• Only implementing basic file stuff for now.
• Not implementing path::absolute right now since absolute UEFI paths
  will not be recognized as absolute path anyway.
• Supports both UEFI shell mapping and device path text representation.
• Follows closely UEFI shell file implementations.

Avoiding directory stuff for now. Also only works for absolute paths.
r? @joboet

[bors]

☔ The latest upstream changes (presumably #130755) made this pull request unmergeable. Please resolve the merge conflicts.

[joboet]

As this is still a draft, I'm assuming you still want to work on it a bit (I'm cleaning up my review queue)?
@rustbot author

[Ayush1325]

@rustbot ready

[Ayush1325]

cc @joboet

[joboet]

I'm truly sorry to keep you waiting for so long – yes, as Nicholas pointed out, this PR is way to large, but I should have informed you of that instead of waiting for the perfect moment to review this PR – which never came. I've been (and am) in your position and know how incredibly frustrating these long delays can be, so I swore to avoid them when I got review permissions. And yet, here we are, so sorry again and I'll promise not to make this mistake again.

I'll happily review smaller patches (within a reasonable time frame, of course), or you could try other reviewers (if I remember correctly, Jubilee has also got a bit of UEFI experience, but I could be wrong).

[Ayush1325]

I'm truly sorry to keep you waiting for so long – yes, as Nicholas pointed out, this PR is way to large, but I should have informed you of that instead of waiting for the perfect moment to review this PR – which never came. I've been (and am) in your position and know how incredibly frustrating these long delays can be, so I swore to avoid them when I got review permissions. And yet, here we are, so sorry again and I'll promise not to make this mistake again.

I'll happily review smaller patches (within a reasonable time frame, of course), or you could try other reviewers (if I remember correctly, Jubilee has also got a bit of UEFI experience, but I could be wrong).

No worries. As a fellow open source contributor and maintainer, I understand these things happen, especially when it's just hobby work.

Thanks for approving the other PR btw. I will try to upstream things in smaller chunks to help with easier upstreaming. This PR is mostly for historical reason now, will close this now in favor of smaller PRs.