Invalid Links in code

[dereuromark]

We have links in code like

@link https://book.cakephp.org/5/en/core-libraries/hash.html#Cake\Utility\Hash::insert

But it cuts off the URL on the \ leaving:

https://book.cakephp.org/5/en/core-libraries/hash.html#Cake

That wouldnt match the anchor on the target page.

I recommend we convert all such FQCN to underscore:

...#Cake_Utility_Hash::insert

Then they work again and are properly clickable in IDE or copy and paste able.

cc @josbeir