rewrite code for optical model that triggers events

[mwetter]

Buildings.HeatTransfer.WindowsBeta.BaseClasses.AbsorbedRadiation and TransmittedRadiation trigger many state events:

The events are caused by the "if" statement and the "integer(x)". This causes about 10 event iterations for each day of simulation, which limits the integration step size (and is expensive).

As a work-around, the "integer(x)" may be avoided if another interpolation is used than the cubicHermite function, or if the whole section between integer(x) and cubicHermite(...)" is put into a function and the smooth annotation is used.

As a test case, enable event logging during simulation and run Buildings.RoomsBeta.Examples.MixedAirFreeResponse

The problematic section is:
{{{
if incAng < 0.5_Modelica.Constants.pi then
x := 2_(NDIR - 1)_abs(incAng)/Modelica.Constants.pi
"x=(index-1)_incAng/(0.5pi), 0<=x<=NDIR";
x := x + 2;
k1 := integer(x) "2<=k<=NDIR+2=HEM+1";
k2 := k1 + 1 "3<=k2<=NDIR+3=HEM+2";

for i in 1:N loop
  // Glass without shading: Add absorbed direct radiation
  y1d := (coeAbsEx[NoShade, i, k1 + 1] - coeAbsEx[NoShade, i, k1 - 1])/2;
  y2d := (coeAbsEx[NoShade, i, k2 + 1] - coeAbsEx[NoShade, i, k2 - 1])/2;
  tmpNoSha := Modelica.Fluid.Utilities.cubicHermite(...

}}}

[mwetter]

[wzuo] Add a smoothInterpolation function to avoid the event. Problem is fixed.