[Multithreaded] Migrate GetPackagesToPrune in SDK

[AlesProkop]

Migrate the GetPackagesToPrune SDK task to support multithreaded MSBuild execution by adopting [MSBuildMultiThreadableTask] and (where required) IMultiThreadableTask with TaskEnvironment for path resolution.

Sub-task of #11835.

Tracking SDK PR: dotnet/sdk#54488

When the linked SDK PR merges, this issue can be closed.