fix: respect trailing slash option when navigating from the root page of the basepath

[eltigerchino]

fixes #11382

The implementation for ensuring the basepath root page always ends with a trailing slash in #10763 is wrong because it was implemented in the load_node method, causing the always trailing slash option to be set on all nodes the root page uses (such as the root layout node), and affecting pages other than the root page. This PR moves the logic closer to where we normalize the URL based on the trailing slash option so we only evaluate the correct trailing slash option after loading the nodes.

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[benmccann]

It looks like the tests are failing

A note that it looks like #11357 fixed the server-side and this is fixing the client side

[eltigerchino]

Tests are fixed now. Targeting the link by its href was a bad idea when there's the base path variable involved

[Coronon]

I just spent 1.5 hours debugging this and was about to submit my own PR when I saw this - thank you for all your work everyone!