Ruby: Introduce With(out)Element MaD input tokens

[hvitved]

This PR adds two new models-as-data input tokens WithElement and WithoutElement, with arguments similar to Element. They translate directly to SummaryComponent::withContent and SummaryComponent::withoutContent calls, respectively.

The new tokens allow us to

1. Get rid of SummarizedCallable::clearsContent(ParameterPosition pos, DataFlow::ContentSet c): this can now instead be expressed as a summary with input Argument[pos].WithoutElement[arg] and output Argument[pos], for a suitable arg.
2. Simplify existing flow summaries that verify that data is stored in a collection, such as Array.new, by replacing read+store with WithElement:
   Before:

        exists(ArrayIndex i |
          input = "Argument[0].Element[" + i + "]" and
          output = "ReturnValue.Element[" + i + "]"
        )
        or
        input = "Argument[0].Element[?]" and
        output = "ReturnValue.Element[?]"

After:

        input = "Argument[0].WithElement[any]" and
        output = "ReturnValue"

3. Give a proper flow summary for the * (splat) operator:

      // *1 = [1]
      input = "Argument[self].WithoutElement[any]" and
      output = "ReturnValue.Element[0]"
      or
      // *[1] = [1]
      input = "Argument[self].WithElement[any]" and
      output = "ReturnValue"

[michaelnebel]

C#: Lgtm

[asgerf]

LGTM