Auxiliary function for projecting "type class dictionary access".
That is, we are trying to extract one of the type class instance elements.
Remark: We do not consider parent instances to be elements.
For example, suppose e is _x_4.1, and we have
_x_2 : Monad (ReaderT Bool (ExceptT String Id)) := @ReaderT.Monad Bool (ExceptT String Id) _x_1
_x_3 : Applicative (ReaderT Bool (ExceptT String Id)) := _x_2.1
_x_4 : Functor (ReaderT Bool (ExceptT String Id)) := _x_3.1
Then, we will expand _x_4.1 since it corresponds to the Functor map element,
and its type is not a type class, but is of the form
{α β : Type u} → (α → β) → ...
In the example above, the compiler should not expand _x_3.1 or _x_2.1 because they are
type class applications: Functor and Applicative respectively.
By eagerly expanding them, we may produce inefficient and bloated code.
For example, we may be using _x_3.1 to invoke a function that expects a Functor instance.
By expanding _x_3.1 we will be just expanding the code that creates this instance.
The result is representing a sequence of code containing let-declarations and local function declarations (Array CodeDecl)
and the free variable containing the result (FVarId). The resulting FVarId often depends only on a small
subset of Array CodeDecl. However, this method does try to filter the relevant ones.
We rely on the used var set available in SimpM to filter them. See attachCodeDecls.