Typescript: Component declaration reference is not recognized by parser

Description

Many Typescript libraries publish types in declaration files (.d.ts) alongside their associated .js bundles. In .d.ts files generated through TS compilation, function types are often defined using declaration references, such as:

declare const MyComponent: React.FunctionComponent<ComponentProps>;

Currently declaration references are not recognized by reactDocgen.parse(). When react-docgen parses a .d.ts file with a single declaration reference, it emits an error: Error: No suitable component definition found..

Desired Behavior

The following code:

import * as React from 'react';

interface ComponentProps {
  foo: string;
}

/**
 * My component is so darn cool!
 */
const Component1: React.FunctionComponent<ComponentProps> = () => <div />;

/**
 * Mine too!
 */
declare const Component2: React.FunctionComponent<ComponentProps>;

Results in the following output:

[
  {
    "description": "My component is so darn cool!",
    "displayName": "Component1",
    "methods": [],
    "props": {
      "foo": {
        "required": true,
        "tsType": {
          "name": "string"
        },
        "description": ""
      }
    }
  },
  {
    "description": "Mine too!",
    "displayName": "Component2",
    "methods": [],
    "props": {
      "foo": {
        "required": true,
        "tsType": {
          "name": "string"
        },
        "description": ""
      }
    }
  }
]

Actual Behavior

The same code results in the following output:

[
  {
    "description": "My component is so darn cool!",
    "displayName": "Component1",
    "methods": [],
    "props": {
      "foo": {
        "required": true,
        "tsType": {
          "name": "string"
        },
        "description": ""
      }
    }
  }
]

Steps to Reproduce

Paste the .tsx sample code from the "Expected Behavior" section into the react-docgen playground with Language set to Typescript.

Start by reproducing the issue in the react-docgen playground with Language set to Typescript, using the .tsx sample and calling reactDocgen.parse() on the declaration reference. Trace the parser entry point for .d.ts declarations and compare the result with the expected output, where Component2 is included with its description, displayName, methods, and props.