It has been detected that, right now, some localised floats are
being passed to those functions (say comma separator, say thousands)
and that's leading to all sort of problems later when comparing,
processing or storing those "wrong-floats" (user entered).

This just makes all those functions to be stricter, so any attempt
of passing to them a wrong float will fail with a clear TypeError.

Any existing case must be converted to a corrrect (X.Y) format, using
unformat_float() or PARAM_LOCALISEDFLOAT before any processing.

Localised floats cannot be used.

Also, fix all the places where those functions are called from
files having strict_types enabled because, with that, now float-like
strings are not accepted any more. Luckily, there is only case,
within the grade/classes/component_gradeitem.php file, and it has
been fixed by casting the float-like string coming from DB to float.