Allow conditional resource manifest args

Summary of the new feature / enhancement

It would be useful to have conditional args passed to resources, like OS or architecture, for example.

Proposed technical implementation details (optional)

Add a new arg object:

{
  "condition": "<expression>",
  "args": [ <args> ]
}

condition would accept a valid expression and args is only appended if condition evaluates to true. Of course, some functions won't be available.

args would be an array and itself can take any valid arg string or object.

No files, tests, or entry points are named. Start by locating resource manifest argument parsing and expression evaluation, then determine how conditional argument objects fit the existing manifest schema. Done means valid conditions append their args, false conditions do not, and supported versus unavailable functions are defined and tested.