Check the size of the strings in the StringPool before flattening.

Test: Tested for normal functionality when string does not exceed
maximum length and tests for detection of string that is too lonhg for
UTF8i
Bug: b/74176037

Change-Id: Ic71d3671a069e7012e8ca107e79e071499eebbf6
(cherry picked from commit a15c2a89)