[llvm] [llvm-cov] Add HTML dark theme support (PR #93080)

[via llvm-commits]

EdJoPaTo wrote:

Now I got a bunch of Emails regarding this merge, not sure what to interpret from that:

https://lab.llvm.org/buildbot/#/builders/188/builds/46756

https://github.com/llvm/llvm-project/pull/93080