Get standardized estimates
Details
For modsem_da, and modsem_mplus objects,
the interaction term is not standardized such that var(xz) = 1.
The interaction term is not an actual variable in the model, meaning that it does not
have a variance. It must therefore be calculated from the other parameters in the model.
Assuming normality and zero-means, the variance is calculated as
var(xz) = var(x) * var(z) + cov(x, z)^2. Thus setting the variance of the interaction
term to 1 would only be 'correct' if the correlation between x and z is zero.
This means that the standardized estimates for the interaction term will
be different from those using lavaan, since there the interaction term is an
actual latent variable in the model, with a standardized variance of 1.