Add chunkModulesSpace property to stats schema

[jaiwanth-v]

Stats doesn't have a chunkModulesSpace property as mentioned in the docs. I have added the property to schema and updated the types. This PR closes #12411.

What kind of change does this PR introduce?
It adds chunkModulesSpace property to stats.

Did you add tests for your changes?
Yes. I've updated the test snapshots.

Does this PR introduce a breaking change?
No.

What needs to be documented once your changes are merged?
None. It's already documented here.

[webpack-bot]

For maintainers only:

• This needs to be documented (issue in webpack/webpack.js.org will be filed when merged)
• This needs to be backported to webpack 4 (issue will be created when merged)

[sokra]

Thanks