Sort the result of SpannableStringBuilder.getSpans

SpannableStringBuilder used to return the result of getSpans in the
order of start indices because of the interval tree it uses. However,
style spans has to be applied in the order of insertion to get
predictable results. Sorted the results of getSpans ordered first by
priority flag and then by insertion time. Moreover improved the
performance of SpannableStringInternal copy constructor.

Bug: 26240132
Change-Id: I0b0fa7bb30a3bd9ca37dedca66d8993718586027