[clang-tools-extra] [clang-doc] Add --asset option to clang-doc (PR #94717)

[Paul Kirth via cfe-commits]

ilovepi wrote:

@nico Actually, I probably shouldn't have reverted. It seems like your GN build is incorrect, and isn't copying the asset files into the right place. The patch that updated that landed in https://github.com/llvm/llvm-project/pull/95187. @PeterChou1 is going to add you as a reviewer on the reland in question, but I think the existing premerge and post-submit bots are sufficient to show that this isn't something affecting the CMake build.

https://github.com/llvm/llvm-project/pull/94717