github: remove some deps on github/graphql.js (#962)

Summary:
A number of modules depended on the legacy `github/graphql.js` module
solely to get at the `Reactions` enum object. As of #961, that object is
exposed from the much lighter-weight `graphqlTypes.js`. This patch
switches over the relevant imports, reducing our dependencies on this
legacy module and its large bundle size.

Test Plan:
It suffices to run `yarn flow` and verify that the two values being
imported are identical.

wchargin-branch: github-use-generated-enums

src/plugins/github/createGraph.js

@@ -6,8 +6,7 @@ import * as N from "./nodes";
 import * as R from "./relationalView";
 import {createEdge} from "./edges";
 import {findMentionsAuthorReferences} from "./heuristics/mentionsAuthorReference";
-// TODO(@decentralion): Opportunity to reduce bundle size
-import {Reactions} from "./graphql";
+import {ReactionContent$Values as Reactions} from "./graphqlTypes";
 
 export function createGraph(view: R.RelationalView): Graph {
   const creator = new GraphCreator();

src/plugins/github/edges.js

@@ -9,8 +9,10 @@ import {
 import * as GithubNode from "./nodes";
 import * as GitNode from "../git/nodes";
 import type {MentionsAuthorReference} from "./heuristics/mentionsAuthorReference";
-// TODO(@decentralion): Opportunity to reduce bundle size (tree shaking?)
-import {Reactions, type ReactionContent} from "./graphql";
+import {
+  type ReactionContent,
+  ReactionContent$Values as Reactions,
+} from "./graphqlTypes";
 
 export opaque type RawAddress: EdgeAddressT = EdgeAddressT;
 

src/plugins/github/edges.test.js

@@ -5,7 +5,7 @@ import {createEdge, fromRaw, toRaw} from "./edges";
 import * as GE from "./edges";
 import * as GN from "./nodes";
 import {COMMIT_TYPE} from "../git/nodes";
-import {Reactions} from "./graphql";
+import {ReactionContent$Values as Reactions} from "./graphqlTypes";
 
 describe("plugins/github/edges", () => {
   const nodeExamples = {

src/plugins/github/graphView.js

@@ -7,8 +7,7 @@ import * as GN from "./nodes";
 import * as GE from "./edges";
 
 import * as GitNode from "../git/nodes";
-// TODO(@decentralion): Opportunity to reduce bundle size
-import {Reactions} from "./graphql";
+import {ReactionContent$Values as Reactions} from "./graphqlTypes";
 
 import {
   Graph,