Full coverage of SN posixlib

[keynmol]

Pre-history: because namespaces don't exist in C or binary world, all the names are globally resolved.

As such, wherever we encounter a symbol from libclang which is a struct or a function, we can check it against the globally known list of structs or functions, and if they exist in Scala Native's posixlib, we should use that name, instead of generating our own code.

We already do it for some types: https://github.com/indoorvivants/sn-bindgen/blob/main/modules/bindgen/src/main/scala/BuiltinType.scala#L29-L66 but the list is woefully incomplete.

1. Find a way to automatically index the posixlib sources of Scala Native
   It would be excellent to use either semanticdb or tasty files served with each
2. Generate the contents of this file: https://github.com/indoorvivants/sn-bindgen/blob/main/modules/bindgen/src/main/scala/BuiltinType.scala#L29-L66 and provide the SBT task to regenerate it

One major requirement is to group the found posixlib definitions by version in which they were introduced.
Bindgen itself can take a parameter to indicate which version it should target.
In SBT plugin that version will be equal to the SN version enabled in the project