Support for fmi3SetInterval and fmi3GetShift APIs for time based periodic clocks

[srivathsanRavi]

Currently the APIs for fmi3SetInterval and fmi3GetShift for implementing time based periodic clocks are not implemented in fmi3Functions.c

fmi3Status fmi3GetShiftDecimal(fmi3Instance instance,
    const fmi3ValueReference valueReferences[],
    size_t nValueReferences,
    fmi3Float64 shifts[],
    size_t nShifts) {
    NOT_IMPLEMENTED
}

fmi3Status fmi3SetIntervalDecimal(fmi3Instance instance,
                                  const fmi3ValueReference valueReferences[],
                                  size_t nValueReferences,
                                  const fmi3Float64 interval[],
                                  size_t nValues) {
    NOT_IMPLEMENTED
}

It would be helpful to have these clock related functions implemented for our applications.