Consolidate our naming around arguments, options, parameters and parameters definition

[alcuadrado]

We need a follow-up PR to #5417 to finish this effort

There are a few things that still need a bit of work:

• Let's use Argument everywhere instead of Parameter. We currently use Argument and Parameter as two different concepts. Argument being the real parameter (compsci lingua for, the actual value that you pass) and Parameter being the formal parameter (the variable that "receives" that parameter). That may be correct, but it's not obvious, and most people use it interchangeably.
• Sometimes, we do have to refer to concepts similar to Parameter (e.g., TaskParameter). Let's use Definition as suffix in those cases. (e.g. TaskArgumentDefinition in that case). This way we make it clear that it's the "formal parameter".