[Feature Request] Expose function to write a model description

[hanneskaeufler]

Seeing as this library already implements the functionality, it was somewhat pointless to reimplement the writing on the users side again.

This could be refactored out like https://github.com/CATIA-Systems/FMPy/pull/451/files#diff-f7a75463637f732e168728bf7998e4c8f8f683206aaf0cfa32867705ec0664edR207

[t-sommer]

What would be the benefit of having this separate function?

[hanneskaeufler]

Writing model descriptions is a task I have to do sometimes. I find the FMPy abstractions to be reasonable, so I prefer to work with the ModelDescription, ScalarVariable types etc. However I don't want to have to implement a function to write a model descriptions based on those types again, seeing as this lib already does that but just doesn't expose it. So: Usage from application code is the benefit

Also: The function to write the container FMU could be factored better and would be easier to understand if it were split up into multiple functions.

[t-sommer]

Something like

def modelDescription2XML(model_description: ModelDescription)
    ...

?

[hanneskaeufler]

Something like

def modelDescription2XML(model_description: ModelDescription)
    ...

?

Yes essentially 👍🏽