• ExpressionAnalyzer: Fix ref.null ht equality check to include ht.
• Precompute: Fix ref.null ht expression reuse to also update ht.
• Fuzzing: Fix ref.null func becoming canonicalized to ref.func $funcref
  when evaluating execution results, by adding a check for isNull.
• Fuzzing: Print actual and expected execution results when aborting.
• Tests: Update if-arms-subtype test in optimize-instructions to check
  that identical if arms become folded while not identical arms are kept.

Fixes #3119