llvm-full: Add version 20.1.1

[Nerixyz]

This adds llvm-full. The main difference to llvm is that this contains headers for Clang and LLVM, static libraries for them, and additional tools like llvm-config (often required when building a tool that interacts with LLVM).

-full might not be the most descriptive suffix. It suggests that all tools from LLVM are included and, to some extent, that these builds are built to support plugin development, but they only contain static libraries for the components. Would love some suggestions.

I have never contributed to a bucket, so I don't know the exact conventions. Since llvm comes in two manifests, I want to replicate that here, because LLVM 19, for example, doesn't include full builds for arm64. Similarly, the beta versions of LLVM 20.1 didn't include a build for arm64 either. Can I include the arm64 version in here, or should I open another PR? I currently just mentioned that llvm-full-arm64 will exist at some point.

Closes #6402

• Use conventional PR title: <manifest-name[@version]|chore>: <general summary of the pull request>
• I have read the Contributing Guide

[github-actions]

All changes look good.

Wait for review from human collaborators.

llvm-full

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