[11.x] feat: restore type-narrowing bahavior for throw_* helpers

[crishoj]

Follow-up to #53154 from yesterday, based on input from @calebdw.

Restore the type-narrowing behavior of throw_if / throw_unless when passed a strictly boolean condition:

/** @var float|int $foo */
throw_if(is_float($foo));
assertType('int', $foo);