This adds the missing unit tests for the conversion functions.
It also extends the type support by adding the `TEXT` type to those functions that support `KEYWORD` already (which also simplifies the testing, actually). Some functions did have it, some didn't; they now all do.
The change also fixes two defects resulting from better testing coverage: `ToInteger` and `ToUnsignedLong` had some missing necessary exceptions declarations in the decorators for the evaluators.
It also updates `ToInteger`'s `fromDouble()` conversion to use a newly added utility, so that the failed conversions contain the right message (`out of [integer] range`, instead of the confusing `out of [long] range`).
Related: #102488, #102552.
