SI-8061 Do not mutate List in Types.scala

  In src/reflect/scala/reflect/internal/Types.scala, change the
  findMember method's algorithm to use the public List API.
  Prior to this change, the method built a list of matching members
  by appending matching symbols and mutating the tail.
  This change builds up the maching list by prepending instead,
  and reverses the result at the end.