Function functionOfExponential

src/compute-engine/rubi/rubi-utils.ts:3375–3380

(u: Expression, x: string)

 * when cosine (with a linear argument) is the SOLE x-dependent trig head, map
 * every `cos[e+f·x] → sin[e+π/2+f·x]` so the integrand routes to the sine
 * chapter (Rubi has no Cosine chapter). Generalizes `unifyInertTrig`'s
 * base-only cos→sin to poly·cos products (`∫(c+d·x)^m·cos`, `∫cos/(c+d·x)^k`).
 * A strict no-op when any other inert trig head is present (mixed cross-pair,
 * handled by the two-factor clauses) or no linear-argument cosine appears. */
export function standaloneCosineShift(
  ce: ComputeEngine,
  e: Expression,
  x: string
): Expression {