[clang] [clang-tools-extra] [clang][NFC] Un-constify `MultiLevelTemplateArgumentList` (PR #104687)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

I'll deal with the formatting later, because I don't want to burden reviewers with more changes than necessary.
I also updated the description after fixing clang-tidy build. We've got two more bad `const_cast`s.

https://github.com/llvm/llvm-project/pull/104687