[Umbrella] Adding Github workflows

[simonsan]

ci: adding windows and ubuntu workflows,
doc: adding status badges for mac and win to readme.md

For the caching there is still some fine-tuning needed in the future. I'm also waiting for an increase of the limit and possibility to cache vcpkg/installed-dir of github-actions (actions/cache#6) and adding vcpkg packages to the virtual env (actions/runner-images#11) and that Qt gets added to the images (actions/runner-images#8). That overall could lower the win build for around 12 minutes.

The Ubuntu-CI is not running inside this main repo, but just outside for any forks of openage. People can make future use of this for pre-diagnosing clang-tidy-errors or clang-format-stuff inside their forked repositories. This functionality (clang-tidy and clang-format) is not added with this PR though and might come in the future.

Win

• Investigate after build test output not being forwarded by shell
• Packaging Nightly builds directly on Github Releases
• Look into install prefix on x64 target being program files (x86) => Around this function (thanks tu) (can't reproduce for now, later?)
• User PWSH interface to Windows Defender to scan package before publishing
• Make use of Compiler Cache (clcache, cclash)
• Add build matrix for cases (versions of Python (Upstream Issue) or included in win environments, versions of compilers)
  • Python
  • MSVC would be a good start into a build matrix => only Visual Studio 2019 on newest Windows builds
  • Architecture is not needed now, but prepared, as we are not building/testing/packaging for 32bit platforms currently
• Add caching for vcpkg-dir using run-vcpkg (example using run-cmake as well)

Win-MSYS2

• MSYS2 could be an easy replacement where we could build on gcc/g++ and clang as well in a build matrix setup (would be easy to cache as well, one folder)
• Packaging Nightly builds directly on Github Releases
• Make use of ccache

Linux

• New make targets
  • Code Analysis: Get clang-tidy script to work and let it upload a fixes-patch as artifact (Add clang-tidy to buildsystem checks #1157)
  • Code Formatting: Get clang-format to work and let it upload a fixes-patch as artifact (Add .clang-format to the repository #1167)
    Ideas:
  • Sanitizer builds?
  • Code coverage reports?
  • VVVerbose builds?
  • Dependency Graph
• Lockfile: Use config for the same system as lockfile so config changes rebuild cache
• File headers: Add header from copying.md to scripts

Mac

• Packaging?
• Add build matrix for cases (versions of Python, versions of compilers)
• Check current workflow for fonts problem
• Wait for the 2 GiB individual cache limit and cache brew+llvm, use brew again to install Qt

[simonsan]

Some thoughts:

[simonsan]

Cache limit for workflows got increased, so we probably could cache the complete Qt and vcpkg dir to make build times smaller.

per-cache limit to 2GB to match the per-repo limit
Ref.: actions/cache#6 (comment)

[simonsan]

(Outdated)