Update cardinality in strings to unicode standard (#4402)

Update cardinality in strings to unicode standard (#4402)

This updates the default cardinality in strings to match the Unicode standard, 196608.

This avoids a check-model failure from 25 benchmarks in SMT-LIB, which were related to a split due to insufficient constants being required during collectModelInfo.

This also makes a few places throw an AlwaysAssert(false) that otherwise would lead to incorrect models. These regardless should never throw, but it would be better to have an assertion failure.