feat(composition): Improve composition errors / subgraph locations

Subgraph locations aren't always reported (i.e. in the case of graphql-js errors during composition). This results in a UX where schema authors are given an error without being told where to resolve it.

To reproduce, compose:

```graphql
type Query @myUndefinedDirective {
hello: String!
}
```

Note the resulting composition errors (`Unknown directive @myUndefinedDirective`) don't contain the subgraph info that would be useful in output.

Start by reproducing the composition example with the undefined directive and inspect the resulting graphql-js composition errors. Trace how subgraph locations are carried into composition output; done means errors such as "Unknown directive @myUndefinedDirective" include the relevant subgraph information.

Written by the indexing model from the issue text.