feat: port media/formats/webm to CMake

[cadubentzen]

Port media/formats/webm to CMake.

• Compiles
• Tests compile and pass

Depends on #1143
Related #1047

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[joeyparrish]

Will review in detail after #1143 lands. Thanks!

[joeyparrish]

formats_webm.lib(mkv_writer.obj) : error LNK2019: unresolved external symbol "public: static __int64 __cdecl shaka::File::CopyFileA(class shaka::File *,class shaka::File *,__int64)" (?CopyFileA@File@shaka@@SA_JPEAV12@0_J@Z) referenced in function "public: __int64 __cdecl shaka::media::MkvWriter::WriteFromFile(class shaka::File *,__int64)" (?WriteFromFile@MkvWriter@media@shaka@@QEAA_JPEAVFile@3@_J@Z) [D:\a\shaka-packager\shaka-packager\build\packager\media\formats\webm\webm_unittest.vcxproj]

I'm guessing this is a Windows macro gone wrong. CopyFileA smacks of the days of Microsoft API variants for ASCII (A) and wide characters (W).

There's a macro in file/file.cc that deals with this, but it may need to be moved to the file.h header instead.

[cadubentzen]

@joeyparrish CI is finally green, please take a look 🙂

[joeyparrish]

Will do. Thanks!

[joeyparrish]

Looks like maybe one mistake. The rest looks good.