* Added peer type resolution for arrays and vectors: the vector type is
   selected.
 * Fixed passing the lhs type or rhs type instead of the peer resolved
   type when calling Value methods during analyzeArithmetic handling of
   comptime expressions.
 * `checkVectorizableBinaryOperands` now allows mixing vectors and
   arrays, as long as one of the operands is a vector.

This matches stage1's handling of `^=` but apparently stage1 is
inconsistent and does not handle e.g. `*=`. stage2 now will always allow
mixing vector and array operands for all operations.