Fix CDS prop nullability if @mandatory is used

[siarhei-murkou]

Hi @daogrady 👋 ,

Since the version 8.0.2, CDS has introduced the new logic for CDS params in CDS functions/actions. Now, we have to use @mandatory annotation instead of setting not null keyword. Whereas not null is still working on CDS entity layer..
Therefore, I have added a check on @mandatory existence in order to determine if the property should/shouldn't be marked as nullable in the compiled TypeScript files.

[daogrady]

Hi Siarhei,

thanks for providing this addition! Looks good on first glance, but there seem to be no tests covering this new behaviour as of now. Can you please add a test checking a mandatory vs a non-mandatory field? A more approachable way of testing has been added recently, where you basically have to write consuming TS code for your generated files. Let me know when you need help writing this test.

Best,
Daniel

[daogrady]

Also, as I have learned today, this feature may still slightly change in the near future. So let's maybe shelf this for now until we know with certainty how @mandatory and not null will turn out.