Make calculate_token_untyped public

[lvboudre]

Fixes: #974

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[github-actions]

cargo semver-checks found no API-breaking changes in this PR! 🎉🥳
Checked commit: 91d2b56

[wprzytula]

I'm reluctant to expose such functions publicly - I'd rather think about the solution that avoids the allocation while preserving type safety.
BoundStatement could possibly be such a solution ( #941 ) - it would allow the values to be serialized only once and you could compute token of such statement without serializing again.

As said here, we are not going to expose unsafe (in the sense of non-type-safety) API.
Instead, we're going to introduce BoundStatement, which will pre-serialize values and thus know its token before execution.