[llvm-branch-commits] [clang-doc][cmake] Copy assets to build directory (PR #95185)

[Paul Kirth via llvm-branch-commits]

https://github.com/ilovepi created https://github.com/llvm/llvm-project/pull/95185

While we copy the asset files, like index.js, into the
correct location in the install step, tests do not have
access to those resources in the build directory.

This patch copies the contents of the clang-doc/assets
directory into the build folder, so that they can be
used in testing.