Skip no-op delta rebuilds for root-local hash indexes

[tnabulsi-netflix]

Summary

• skip HollowHashIndex delta reindexing when the index is root-select and all match fields are direct non-reference fields on the root type
• keep the existing rebuild-on-every-delta behavior for traversing or reference-based hash indexes
• add regression tests covering skipped rebuilds, rebuilds on root changes, and unchanged behavior for non-root-local indexes

Testing

• ./gradlew :hollow:test --tests com.netflix.hollow.core.index.HollowHashIndexTest --rerun-tasks -Pcom.netflix.gradle-predictive-test-selection.enabled=false

[azeng-netflix]

This part is not needed, as ordinal change is a direct signal on whether or not a hash needs to rebuilt.
One reason is that, for top level type A, if its member type B has a field change, the change would cause the type A record to have an ordinal change as well.
This statement holds true, also because:

1. for a type, an ordinal will not be reassigned within a single cycle.
2. Hollow Data set version update via delta would apply every delta on the version chain, and would not skip a version.
3. a sub type's ordinal change would propagate all the way up to the top level type, all the record along the hierarchy would get assigned a new ordinal.

But also wonder if there are other edge cases..

[azeng-netflix]

@azeng-netflix need to check if double snapshot scenario is also handled and add unit test that would check this invariant in the future.