Analyzer incorrect non-constant nullaware list/set element

[lrhn]

Example:

void main() {
  const b = identical(1, 1.0);
  const Object? v = b ? 0 : null;
  const l1 = [?v]; // OK, a `?v` is a constant expression.
  const l2 = [if (b) ?v]; // Not OK here?
  const l3 = [if (b) v else ?v]; // Not OK here?

  const s1 = {?v}; // Different bug!
  const s2 = {if (b) ?v}; // Not OK here?
  const s3 = {if (b) v else ?v}; // Not OK here?
}

The ?v in l2, l3, s2 and s3 makes the analyzer say

The values in a const list literal must be constants.

It has no issue treating the same ?v element as constant outside of a conditional. The CFE accepts the program.