alt.use

`alt.use`

Always use `alt` to display equations

## Description

When an (informal) equation contains both `alt` and another element (graphic, etc.), and when `tex.math.in.alt` is not set to 'latex', the alt element is not used to display the equation since it is considered as a fallback element. Set `alt.use` to force the use of `alt` as default rendering element even when `tex.math.in.alt` is not set to 'latex'.