Configuration option to disable fallback transitions in SPA mode

Problem/Motivation

The fallback transition animation for browsers that don't support the view transitions API is hopefully better than nothing, but it isn't as good as the real deal. Users may prefer to disable these. In this case, I wonder if we should enable client side routing entirely. Also wondering if this should be off by default.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes