[ffigen] Separate getDartType and getUserType (#623)

* Separate getDartType and getUserType

* Fix analysis

* Document instancetype special casing

* s/getDartType/getFfiDartType

* s/getUserType/getDartType
13 files changed
tree: 5d6102526ebc4a52f40dcf2b340282cc2ec328ed
  1. pkgs/