Refactor AppVeyor configuration

[EwoutH]

This PR refactors the AppVeyor configuration. Since it's quite a large PR, I split is up into 3 commits:

• Refactor AppVeyor configuration
  • Updates environment to the Visual Studio 2019 image (running on Windows Server 2019)
  • Make a shallow clone, which is faster and smaller, of libde265-data with --depth 1
  • Use msbuild instead of cmake --build
  • Build Release configuration (instead of Debug)
  • Remove x86 job
  • Publish individual .exe and .dll artifacts
• AppVeyor: Add Arm64 build
  • Adds a Arm64 build
  • Runs the tests only on the x64 build
• AppVeyor: Allow Arm64 job to fail

The first commit is in fact the full refactor for the x64 platform. The second commit adds an run targeting the Arm64 platform, and the third commit allows the Arm64 build to fail. That last one is a separate commit so that it can be easily converted when the Arm64 build pass.

My development branch can be viewed here for even more granular changes.

[EwoutH]

Hi @farindk and @fancycode, any chance one of you could review this PR?

[EwoutH]

@farindk @fancycode I'm doing some cleanup of old, open PRs. If you would like to get these changes in, please leave a reply or review.

In two weeks I will close this PR if no reaction received.