New command-line APIs and offline argument

[NikolaMilosavljevic]

This PR provides several improvements in sourcelink tool:

• Adds --offline argument for test option - enables test option in offline scenarios
• Fixes Make dotnet-sourcelink source-buildable #1028 - enables tool to be built in source-build
• Updates command-line-api dependency to match what's used in source-build, and all other repos that have that dependency
• Converts command-line usage to new API model, as required by updated command-line-api dependency - same work that was recently done in other repos, i.e. dotnet/sdk@6483a69

[NikolaMilosavljevic]

@tmat

[NikolaMilosavljevic]

@dotnet/source-build-internal