Draft: testing/dotnet31: upgrade to 3.1.419

• upgrades dotnet31-sdk to 3.1.419
• upgrades dotnet31-runtime to 3.1.25
• build against icu-data-full
• move to /usr/lib/dotnet
• merge dotnet31-sdk with dotnet31-build

edit

Following part of the update has been cancelled due to broken build of reference packages on current state of edge. Might come back to this at a later point once I have more time

• upgrades dotnet31-stage to 3.1.419
• merge dotnet31-bootstrap with dotnet31-stage0
• make dotnet31-build buildable upon itself