feat: port HLS module to CMake

[cosmin]

Related to issue #1047

[cosmin]

rebased now that cmake port of mpd has landed, next I'll need to address some of the same feedback from the MPD branch here (starting with FlagSaver)

[cosmin]

My clang-format locally and the Github Actions clang-format seem to be doing different things for this change in GenerateSegmentUrl. For now I applied the patch out of the failing Github Actions check locally.

[joeyparrish]

Looks good, except for Windows build failures like:

packager\hls\base\simple_hls_notifier.cc(239,16): error C2664: 'bool shaka::hls::MediaPlaylist::WriteToFile(const std::string &)': cannot convert argument 1 from 'std::filesystem::path' to 'const std::string &'

[cosmin]

the problem is that on Windows there is no implicit conversion of std::filesystem::path to std::string (instead on Windows it can convert to std::wstring) whereas on Linux/Mac there is. Going to take a few iterations to flush out all usages by waiting for the Windows checks to run.

[cosmin]

Fixing docs build in #1257