Replace bat files with NUKE build

[lahma]

While getting Fluid to build I was once again faced with all sorts of build script problems, like location of MSBuild/Visual Studio etc (required VS developer command prompt to have PATH right).

NUKE allows you to create build script using plain C# with great API and reduced risk of typos. Library also gives you full power of C# (loops, functions, encapsulation, variables and typing). It's really easy to adopt if you know C#.

What I offer with this PR:

• new solution project _build.csproj
• all build logic neatly in Build.cs, should be quite readable
• transform build\*.bat files to call relevant NUKE targets, new targets in Build.cs contain the old bat file logic
• build.cmd and build.sh at repository root, easy to get started (Linux build possibility!)

FUTURE

• NUKE can generate appveyor, github actions, teamcity etc CI configurations if needed, no need to fight YAML
  • same targets can be invoked with appveyor, azure devops and github actions
• build on linux (needs some tweaks for targets / ignores), I've done this with multiple projects
• this will also benefit Improve build and reduce warnings #3437 and Replace DotLiquid with Fluid #3679

Targets can be invoked using Windows command line with build.cmd (default compile), build.cmd unittest (UnitTests.bat functionality), configuration is automatically Release in CI environment (not a local build).

[lahma]

@RicoSuter do you think we could change like this in as part of larger changes that are currently in motion. This would modernize and enable new scenarios, like testing on Linux.

[lahma]

I've added basic sample how to add GitHub actions workflow generation (Build.CI.GitHubActions.cs), now pr and build, could add different rules and invocations like "push to preview MyGet on master build", could probably also add release workflow that is only triggered when tags are being created.

I'm afraid I cannot test these as these require a bit more permissions in the repo for GitHub to allow running such code.

[RicoSuter]

Ok, ill have a look. Can i merge this PR and then continue with that?

[lahma]

Yes please, ping me if there's anything problematic you find.

[lahma]

The GitHub actions should light up after the merge, normal contributors cannot trigger workflow changes via PRs as it's a security risk.

[lahma]

@RicoSuter I've pushed couple PRs to fix two issues found by CI runs