Make SuggestionRangeSpan public

when we have overlapped SuggestionSpans, the
range of text being replaced can change depends on
the number of suggestions in the SuggestionSpans, so
accessibility services need to know the text being replaced.
We send text change event with the before text doesn't have the
SuggestionRangeSpan and after text has the SuggestionRangeSpan,
so a11y services can inform the user about the text being
replaced.
Other ui toolkits like compose can convert their style indicating
text being replaced to SuggestionRangeSpan.

Bug: b/143378480

Test: tested the event is sent.

Change-Id: I6d0d33e46f7c8ac9dbcc177ab54718184e715fb6