Support alternative type coercion mode in recursive traversals

[obi1kenobi]

Fully analogous to #784, except for type coercions:

{
    Foo {
        out_Foo_Bar @recurse(depth: 3) {
            ... on Baz {
                name @output(out_name: "name")
            }
        }
    }
}

The ... on Baz type coercion could either be applied fully after expanding the recursion (option 1) or could be applied at each step of the recursion (option 2).

Here we unfortunately don't have the freedom of simply adding a field to an existing directive, as in the @filter case in #784. We may need to define a custom directive (e.g. @type_coercion_mode) that only applies to type coercions. We can set it to be only valid on INLINE_FRAGMENT AST locations, but we'll need to validate that the inline fragment in question is immediately within a @recurse.