This introduces a dedicated getter to extract call descriptors from
operators of call nodes (i.e. call and tail-call) to ensure that all
accesses are const-correct. An implicit cast of constness is undefined
behavior and hard to spot without sanitization.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/1894983002

Cr-Commit-Position: refs/heads/master@{#35570}