Reduce redundancy in the RequestGraph's Request, Env, and Option nodes

[gorakong]

↪️ Pull Request

Continued from #9360. This PR reduces redundancy in the RequestGraph's Request, Env, and Option nodes by getting rid of the value object in each of them, since these can be derived from their IDs. On a large app, this nets us a further ~7.1% reduction in the size of the serialized RequestGraph.

💻 Examples

Request Nodes

Before:

  {
    id: 'f20cf057afed92f9:Main',
    type: 'request',
    value: { id: 'f20cf057afed92f9:Main', type: 'path_request' },
    invalidateReason: 0
  }

After (Request Nodes still maintain a request type, but their subtypes can be distinguished via requestType):

 {
    id: 'f20cf057afed92f9:Main',
    type: 'request',
    requestType: 'path_request',
    invalidateReason: 0
  }

Env Nodes

Before:

  {
    id: 'env:NODE_ENV',
    type: 'env',
    value: { key: 'NODE_ENV', value: 'production' }
  }

After:

 { id: 'env:NODE_ENV', type: 'env', value: 'production' }

Option Nodes

Before:

  {
    id: 'option:shouldBuildLazily',
    type: 'option',
    value: { key: 'shouldBuildLazily', hash: 'false' }
  },

After:

{ id: 'option:shouldBuildLazily', type: 'option', hash: 'false' }

[JakeLane]

💯

[JakeLane]

nit: It might be better to build a mock typecast so there's no any type created by the suppression, which would mean the test won't break if the types change

Something like:

async function mockRunRequest(
      tracker: RequestTracker,
      request: {...Request, type: Request.type | 'mock_request', ...},
      opts?: ?RunRequestOpts,
    ): Promise<TResult> {
      return tracker.runRequest(request, opts);
    }

[gorakong]

Good call @JakeLane! Let me know what you think about how I mocked runRequest (wasn't sure if that was the best way)

[gorakong]

@JakeLane just FYI I ended up changing all the mock_requests to be one of the types in the RequestType union. When I tried mocking the types (53fdf80), the only way I found that appeased Flow was to do it in a way that essentially did the same thing (as above) 😅