mtlb_int32 Matlab int32 emulation function

## Description

Matlab and Scilab `int32` behave differently :

- Beyong the main interval bounds, Scilab's `int32()` wraps, while Matlab's `mtlb_int32()` saturates.
- For non integer values, Scilab's `int32()` truncates the fractional part, while Matlab's `mtlb_int32()` rounds to the nearest integer.

Let `imin = -(2^16) = -2147483648` and `imax = 2^16 - 1 = 2147483647`.

x | int32(x) | mtlb_int32(x)
--- | --- | ---
%nan | 0 | 0
-%inf | imin | imin
imin-2 | imax-1 | imin
imin-1 | imax | imin
imin | imin | imin
imin-1 | imin-1 | imin-1
-80.7 | -80 | -81
-80.5 | -80 | -81
-80.4 | -80 | -80
10.2 | 10 | 10
10.5 | 10 | 11
10.51 | 10 | 11
imax | imax | imax
imax+1 | imin | imax
imax+2 | imin+1 | imax
imax+3 | imin+2 | imax
%inf | imax | imax

`mtlb_int32` has not to be used for hand coded functions.

The function `mtlb_int32(A)` is used by `mfile2sci` to replace `int32(A)` when it is not possible to know what is the input while porting Matlab code to Scilab. This function then determines the correct semantic at run time.