Allow SDC `get_*` with 0 args and on object references

[akashlevy]

This PR adds two features into SDC processing:

• get_* with no arguments is interpreted as get_* *
• get_* called on SWIG object references *_p_<objtype> will keep those references intact rather than failing

Let me know if anything should be added to the docs for these changes.

[jjcherry56]

You need to type check the objects: get_pins [get_cells] _e001650300600000_p_Instance _8001650300600000_p_Instance _6000650300600000_p_Instance _2001650300600000_p_Instance _c000650300600000_p_Instance

I would prefer it if you did not use continue. Please break the tests into 2 tests; one for no arg and the other for passing objects.

[akashlevy]

Sure, will do these tonight

[akashlevy]

Ok, made the changes:

• I added error messages for when the type is wrong and updated messages.txt
• Switched from using continue to else { ... }
• Split into test cases for get_noargs and get_objrefs

[akashlevy]

Let me know if anything else is needed :)