Remove support for relative paths in static resource handling

[rstoyanchev]

Following thes updates to URL parsing in #33639, it's clear that with the WhatWg URL Living Standard spec, there is no good reason to expect URL paths that are not normalized. Those have been a source of security issues, and while we have protections against them in static resource handling, and they are also rejected by the Spring Security firewall, we can now drop support for them altogether going forward.