NuGet client code needs some refactoring

[jainaashish]

Multiple places in current NuGet code needs refactoring to better align with their meaning. Currently they are poorly named or explained or designed. This is the uber issue to keep track of such instances and look for the opportunity to improve those in future releases.

• LockFile which has nothing to do with a lock file instead represent assets file (project.assets.json or project.lock.json)

• PackageSpec which again has nothing to do with a package instead it's kind of projectSpec or all the relevant details about the project NuGet needs for restore

@NuGet/nuget-client please keep on adding more n more such instances here.

[aidapsibr]

I also would like to recommend facades. The code is incredibly hard to reason about and harder still to use all the constituent parts correctly to end up in "default" behavior. If this is not in line with the spirit of the issue feel free to thumbs down. 😅

[nkolev92]

Unlikely to make these binary breaking changes at this point. We can easily reopen an issue if we decide to change this.