Audit log should not save properties those were not changes

[hikalkan]

see #3713

[maliming]

Caused by #2652

It seems that propertyEntry.IsModified is incorrect.

This judgment is also incorrect if the entity is not tracked.
OriginalValue is always equal to CurrentValue.

var isModified = !(propertyEntry.OriginalValue?.Equals(propertyEntry.CurrentValue) ?? propertyEntry.CurrentValue == null);

[maliming]

@hikalkan Should I revert #2652?