[OSS v13 Compiler] Generate exact imports when using CommonJS and output

[bigfootjon]

The old JS compiler would generate exact foo$fragmentType imports when artifactDirectory is set since this allows the compiler to know where all the artifacts would be (all in the same directory).

The new compiler does not appear to support this currently. But this seemed easy enough to do, so I've taken a stab at it in this diff. I am not fluent in Rust (yet) so I am happy to take criticism on how to write this better!

Test plan:
cargo test passes

cargo run --bin relay -- ../../../myproject/relay.config.json produces the expected output.

Example file diff from the rc0 version of the compiler to this PR/Diff:

diff --git a/__generated__/BlogPostPageQuery.graphql.js b/__generated__/BlogPostPageQuery.graphql.js
index 96bd4fbf6..2911ddbd7 100644
--- a/__generated__/BlogPostPageQuery.graphql.js
+++ b/__generated__/BlogPostPageQuery.graphql.js
@@ -1,5 +1,5 @@
 /**
- * @generated SignedSource<<e8ed1071e6aabf5e4f69fd2c87674a6b>>
+ * @generated SignedSource<<f722c4d69fbe60872e2b896ecba50897>>
  * @flow
  * @lightSyntaxTransform
  * @nogrep
@@ -12,7 +12,7 @@
 
 /*::
 import type { ConcreteRequest, Query } from 'relay-runtime';
-type BlogPost_post$fragmentType = any;
+import type { BlogPost_post$fragmentType } from "./BlogPost_post.graphql";
 export type BlogPostPageQuery$variables = {|
   relativePath: string,
 |};

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