Restructure PackageService to better support endpoints requiring all versions of an ID

[scottbommarito]

precursor to #6773

Both PackagesController.DisplayPackage and PackagesController.Manage require all versions of a package.

Previously, this was done either implicitly or lazily, specifically:

• if a version isn't specified or is missing, FindPackageByIdAndVersion must fetch all versions to calculate the latest one
• if a version was specified and found, the remaining versions would be loaded lazily

This is bad because our perf for these endpoints are relying on a hidden behavior of one of our services, and when this hidden behavior doesn't go our way, lazy loading is very very very very slow, and adding the deprecation entities associated with this feature makes it even worse.

So, to remedy this

• add FindPackagesById to get all packages by ID (with a withDeprecations parameter for when deprecation entities are needed)
• move logic from FindPackageByIdAndVersion that fetches the latest version from a list of packages and move it into FilterLatestPackage
  • FindPackageByIdAndVersion now calls FilterLatestPackage internally
• make DisplayPackage and Manage call FindPackagesById and then FilterLatestPackage if an exact version isn't found
• move the code from FindAbsoluteLatestPackageById into DisplayPackage

[joelverhagen]

Address comment then

[skofman1]