Infer scope only on parameters with pointers

[dkorpel]

Trying to fix dlang/ddox#239

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Testing this PR locally

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dub run digger -- build "master + dmd#15116"

[dkorpel]

Buildkite is green now, great!

[PetarKirov]

Can you add a tests for this? Perhaps one that checks this on the language level with static assert and one that checks this in the JSON output (that ddox consumes).

[RazvanN7]

I merged this to unblock buldkite. The tests can be added in a subsequent PR.