Add handler for packages.lock.json in nuget

[TG1999]

Reference: aboutcode-org/scancode.io#1263

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[AyanSinhaMahapatra]

Thanks++ @TG1999

See comments for a few questions and changes.

Also, typically we have lockfiles beside another package manifest right?
I was looking for examples of this and is this .csproj files for nuget? Are there other manifests which would be nice to parse and store?
Here is an example of a .csproj file and packages.lock.json together: https://github.com/ncblakely/GiantsTools/tree/main/Giants.Services to add as tests.
Should we not also do some lightweight package assembly here?

[TG1999]

Adressed all review comments, feel free to merge.

[AyanSinhaMahapatra]

LGTM!
Thanks++ @TG1999 merging!