reworked dotnet (and deps)
Changelog:
- removed: visual-studio-code - replacement: app-editors/vscode
- added: dev-dotnet/dotnet-sdk-shared
- added: dev-dotnet/dotnet-runtime-nugets
- added all current and legacy dotnet related packages (except non-binaries) in an upsteram compatible way
- changed all ebuilds to match "upstream" patterns
- changed package.mask and removed package.use
WARNING: Not yet 100% tested!