Update scripts and packaging to support .NET 5.

[pchote]

Adds compatibility for OpenRA/OpenRA#17989, OpenRA/OpenRA#18955, OpenRA/OpenRA#19026, OpenRA/OpenRA#19325, OpenRA/OpenRA#19389, OpenRA/OpenRA#19413. Filing as a draft now to help mods that want to track bleed, but this shouldn't be merged until we are ready to tag the next upstream prep branch.

[pchote]

When looping over ${PACKAGING_COPY_MOD_BINARIES} we also need to copy the .deps.json! (pdbs too). This otherwise breaks for mods that rely on any external dlls.

[pchote]

Scratch that - the whole approach of copying files out of engine/bin appears to be bogus and cause runtime crashes for OpenKrush. Changing this to use dotnet publish on the SDK sln should hopefully fix this.

[pchote]

The mono checks at the start of the launch scripts need to be updated to work with dotnet only setups.

[pchote]

Need to rebase on latest bleed and add the --self-contained publish flag.

[OndroNR]

There is missing dotnet check (as mono alternative) in utility.sh at start

[pchote]

Updated for OpenRA/OpenRA#19389.

Updated test build: https://github.com/pchote/OpenRAModSDK/releases/tag/devtest-20210718

[Mailaender]

While you are at it maybe add an empty SoundFormats: as well?

[Mailaender]

This will install global mix database.dat even when PACKAGING_COPY_CNC_DLL="False". In the past you could simply remove it from PACKAGING_COPY_ENGINE_FILES.

[pchote]

The PACKAGING_COPY_ENGINE_FILES change happened in the last release (IIRC), and fixing it properly will require non-trivial changes to the upstream engine (allowing mods to specify a path to the mix database instead of assuming it is available in the engine root). It won't be possible to address that here.

[penev92]

Superseded by #180.