Timestamp type mismatching between Trino and Velox

For Trino:
- ShortTimestamp (a Long member, 64 bits)
- LongTimestamp (a Long member and an Int member, 96 bits)

For Velox:
two Long members (128 bits)

```Timestamp(Precision)``` type signature in Trino specification is not supported in Velox

 Some related UTs are disabled in ```TypeSignatureTest.cpp```