Getter of a primary value of an inline class belongs to the box class.
Its arguments should not be unboxed when the method is called.
However, its result might require boxing if it's an inline class value.
When we have an internal primary value, there's no getter method.
In fact, we can use box/unbox methods for inline class directly
(don't forget to box the result, it may be an inline class type value).
#KT-26748
Mikhael Bogdanov