Add explicit instantiation declaration for ScalarValue<double> and ScalarValue<float>.
Add explicit instantiation declaration for ScalarValue<double> and
ScalarValue<float>.

vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa