Migrate documentation for all core functions from scalar_functions.md to code

[Omega359]

Is your feature request related to a problem or challenge?

As part of #12740 this ticket is to migrate all the existing documentation for core functions from the scalar_functions.md file to code and to remove from the scalar_functions.md file. In addition sql examples should be added for all of the updated functions.

This includes:

• arrow_cast
• arrow_typeof
• coalesce
• named_struct
• nullif
• nvl
• nvl2
• struct
• version

documentation should also be added for get_field which currently is not documented.

Describe the solution you'd like

No response

Describe alternatives you've considered

No response

Additional context

No response

[Omega359]

take

[alamb]

@Omega359 do you think we/I should fix tickets for the other function catagories (to start parallelizing this work?)

[Omega359]

Sure! I was going by modules which do not line up perfectly with the sections in the docs but it shouldn't be that much of an issue. Otherwise I expect if I churn through them it'll be a week or two before I'm done.

[alamb]

Sure! I was going by modules which do not line up perfectly with the sections in the docs but it shouldn't be that much of an issue. Otherwise I expect if I churn through them it'll be a week or two before I'm done.

I filed #12828 and #12827 to start things off. We'll see how that goes and then I can file some more