[SDC] Input/Output delay for All ports -> script writing

If you read_sdc first, you can only do a syntax check. If you do it in the other order, you can apply the constraints as they're read in, which in some cases is necessary.

If the only thing you ever ran was read_sdc, then update could be implied, but it's possible to do read_sdc and then something like "read_sdc uncertainty_constraints.sdc", i.e. read a file that is not automatically pulled in by the project. Seldom done, but since it's a script it's better to break out the options. In the GUI, if you click on any of the reports then all three are done automatically in the correct order.