Reload preloaded libraries only if there are new packages to load

[aparajit-pratap]

Purpose

This is a small optimization to avoid having to reload all preloaded (out of the box) libraries (zero touch + DS files) IF there are no packages to be loaded.

The first time all preloaded libraries are loaded is during the instantiation of DynamoModel here:

Dynamo/src/DynamoCore/Models/DynamoModel.cs

Line 733 in 43e501e

ResetEngineInternal();

Next, when packages are loaded in the PackageManagerExtension here:

Dynamo/src/DynamoPackages/PackageManagerExtension.cs

Line 155 in 43e501e

LoadPackages(startupParams.Preferences, startupParams.PathManager);

the VM is re-initialized, and all libraries (preloaded libraries + packages) are reloaded again (due to existing VM limitations). This happens even when there are no local packages to be loaded and is wasteful to do twice for preloaded libraries. The change here is to skip reloading preloaded libraries when there are no packages to load.

Declarations

Check these if you believe they are true

• The code base is in a better state after this PR
• Is documented according to the standards
• The level of testing this PR includes is appropriate
• User facing strings, if any, are extracted into *.resx files
• All tests pass using the self-service CI.
• Snapshot of UI changes, if any.
• Changes to the API follow Semantic Versioning, and are documented in the API Changes document.

Reviewers

@mjkkirschner

FYIs

@QilongTang