[CX] Incorrect output type of secondary index keys

The computed output type of the secondary index keys do not take into account whether the keys can be missable/nullable. This can result in producing incorrect tuples.
The below methods need to be checked/fixed:

KeyFieldTypeUtil.getBTreeIndexKeyTypes()

Index.getNonNullableOpenFieldType()

Index.getNonNullableType()

Index.getNonNullableKeyFieldType()