Fixes issues with url rewrites created on shop with multiple storeviews

[hostep]

We have a project where we import a bunch of categories and products programmatically.
And after that we let the url rewrites being created as this doesn't seem to happen automatically.

In Magento 2.1.2, there are problems in the category urls when we do this, where the url's use the url_key from the category data from store id 0 (admin values) instead of from the specific storeview we try to generate the url rewrites for.

This PR fixes our issues.

Possibly related to #4112 and #2619

[magento-cicd2]

All committers have signed the CLA.

[comdiler]

Looks like integration tests are not working. Access denied for user 'root'@'localhost' (using password: NO)
I believe we should wait while it get's fixed :-(

[hostep]

I just updated the PR, my initial commit started giving problems when saving a category in the backend which then threw URL key for specified store already exists. exceptions.
This PR might now also be related to #6671

Would be great if this PR can get some extensive testing, because I'm not total sure if this won't have negative effects elsewhere.

[hostep]

And added a third commit for yet another issue we ran into.
I'm still very unsure about these changes ...

Also: I know the CI tests fail, but I only tested these changes on 2.1.2 and not on the develop branch, I just copied the changes into the new ProductScopeRewriteGenerator.php file, since the logic was moved there from the ProductUrlRewriteGenerator which was being used in 2.1.2

[hostep]

I'm giving up on this, the fixes are never 100% correct in all different cases in which url rewrites can be generated.