`Extract_projections`

Identify projections from variables used in function bodies (free variables or specialised args, for example, according to `which_variables`

below). Projections from variables that are also used boxed are not returned.

```
val from_function_decl :
env:Inline_and_simplify_aux.Env.t ->
which_variables:Flambda.specialised_to Variable.Map.t ->
function_decl:Flambda.function_declaration ->
Projection.Set.t
```

`which_variables`

maps (existing) inner variables to (existing) outer variables in the manner of `free_vars`

and `specialised_args`

in `Flambda.set_of_closures`

.

The returned projections are `projecting_from`

(cf. projection.mli) the "existing inner vars".