Upstream TrenchBoot as Anti Evil Maid - UEFI boot mode support to GRUB2

[BeataZdunczyk]

Brief summary

Upstream the code implementing TrenchBoot UEFI boot mode support to the official GRUB2 repository.

• Initial Patchset Submission: Submit the initial patchset implementing TrenchBoot UEFI boot mode support to the GRUB2 mailing list: GRUB-devel.

• Developing Fixes: Implement additional fixes based on the latest round of feedback.

• Refreshing Code: Ensure the code remains up-to-date with any recent changes in the GRUB2 repository.

• Communication and Collaboration: Continue active communication with the GRUB2 community and maintainers.

[SergiiDmytruk]

https://github.com/TrenchBoot/grub/commits/refs/heads/tb-rebase-2025.05/ is the rebased branch. Rebasing onto the latest upstream's master on its own didn't require much changes, but we have accumulated a bunch of commits with various fixes and improvements that had to be integrated into previous ones (including chainloader changes used for Xen EFI boot).

Looked at https://github.com/TrenchBoot/grub/tree/grub-sl-2.12-v13 and aligned changes with that a bit (file renames and mle_entry field move, but not moving of SLRT table registration function as that breaks legacy build). I've also done a couple of renames, stylistic and comment corrections which can be seen at https://github.com/TrenchBoot/grub/compare/tb-rebase-2025.05-pure..tb-rebase-2025.05. Some commit messages were updated, but GitHub won't show that.

As usual, Linux patchset (v13 being the latest) is impeding upstreaming.

[SergiiDmytruk]

Links to the latest patchsets which come with UEFI changes are in: #38 (comment)