- Adds `LanguagePrimitives.IsNullLike()` method to account for `DBNull.Value` and `NullString.Value` so that they can be considered the same as a null value where sensible in PowerShell.
- Updates `-ne` and `-eq` binders to treat `DBNull.Value` and `NullString.Value` as equal to null/AutomationNull.
- Update code paths for comparing objects in LanguagePrimitives to ensure consistency with how the `-eq` and `-ne` binders work when calling LanguagePrimitives methods to do the comparisons.
- Make `LanguagePrimitives.IsNull()` and `LanguagePrimitives.IsNullLike()` public methods.
- Added tests for null behaviours in `NullRepresentatives.Tests.ps1`
