Support Debug for describe blocks

[mfulton26]

Environment

1. node -v: v8.9.4

2. npm -v: 5.6.0

3. npm ls react-scripts (if you haven’t ejected): `-- (empty)

4. Operating system: Windows 10

Steps to Reproduce

Create a describe block with multiple test. e.g.:

describe('x', function() {
  test('1', function() {
  });
  test('2', function() {
  });
});

Expected Behavior

A CodeLens to "Debug" appears for the describe block and one for each test.

Actual Behavior

A CodeLens to "Debug" appears only for each test and not for the describe block.

[seanpoulter]

Neat idea Mark. Do you want to try your hand a PR for it @mfulton26?