Add "generate_path_property" option

[sin-ack]

This replicates the behavior of <PackageReference GeneratePathProperty="true" /> in Paket. This is required in certain edge cases, such as when creating a source generator project that needs to reference third-party assemblies.

Tests have been added for verifying the option in the lockfile, paket.dependencies/paket.references files and to verify the output in the generated paket.props files.

[sin-ack]

Hmm, I learned after opening this that apparently it is possible to enable this without Paket integration using ItemDefinitionGroup:

<ItemDefinitionGroup>
  <PackageReference>
    <GeneratePathProperty>true</GeneratePathProperty>
  </PackageReference>
</ItemDefinitionGroup>

If this PR is unnecessary after this, feel free to close it.