[clang-tools-extra] reapply [clang-doc] Add --asset option to clang-doc (PR #96358)

[Nico Weber via cfe-commits]

nico wrote:

(I now ported ade28a77ed17760bf2fde57c6571b69489b0bac0 to the GN build in 3ba7599842be. Again, apologies for missing this – the GN build shouldn't affect other people. But I'm kind of glad it did since I found several GN-unrelated issues both here and on #93928. Feel free to do with them what you will – except for the stdexcept include over in #93928, please remove that)

https://github.com/llvm/llvm-project/pull/96358