Rollup merge of #135475 - Ayush1325:uefi-absolute-path, r=jhpratt

uefi: Implement path

This PR is split off from rust-lang/rust#135368 to reduce noise.

UEFI paths can be of 4 types:
1. Absolute Shell Path: Uses shell mappings
2. Absolute Device Path: this is what we want
3. Relative root: path relative to the current root.
4. Relative

Absolute shell path can be identified with `:` and Absolute Device path can be identified with `/`. Relative root path will start with `\`.

The algorithm is mostly taken from edk2 UEFI shell implementation and is somewhat simple. Check for the path type in order.

For Absolute Shell path, use `EFI_SHELL->GetDevicePathFromMap` to get a BorrowedDevicePath for the volume.

For Relative paths, we use the current working directory to construct the new path.

BorrowedDevicePath abstraction is needed to interact with `EFI_SHELL->GetDevicePathFromMap` which returns a Device Path Protocol with the lifetime of UEFI shell.

Absolute Shell paths cannot exist if UEFI shell is missing.

cc `@nicholasbishop`

Author: matthiaskrgr