'GetClassDefaults' Can Cause Blueprint To Become Modified When Unrelated Blueprint Is Compiled

The stems from a really old change (CL 2948683) to fix [Link Removed].

Compiling ObjectA will call RefreshExternalBlueprintDependencyNodes on its dependent BP, 
ObjectB_ReferencesA, which reconstructs the nodes. After this call, we remove the dirty flag from ObjectB_ReferencesA. This is why ObjectB_ReferencesA is not marked for dirty.

Additionally, ObjectB_ReferencesA is recompiled because its a dependent BP of ObjectA. After compilation, ObjectC_UsesClassDefaultsB is notified via the OnBlueprintCompiledDelegate delegate. The delegate reconstructs the GetClassDefaults, which dirties the package.

1. Open the Blueprint editor in any project
2. Create a BP object named ObjectA, which is empty with no references
3. Create a BP object named ObjectB_ReferencesA, which references A with any node on any graph (ex. a ConstructObjectFromClass with ObjectA)
4. Create a BP object named ObjectC_UsesClassDefaultsB, which uses GetClassDefaults on ObjectB_ReferencesA on any graph)
5. Compile and save the new files.
6. In ObjectA, add a new variable of any type and hit compile.
7. Observe that ObjectC_UsesClassDefaultsB is marked dirty, but ObjectB_ReferencesA isn't.
8. Expected behavior: neither ObjectC_UsesClassDefaultsB nor ObjectB_ReferencesA is marked as dirty.