fix(react-router/router): compatible with `createRouter` where `basename` does not start with `/`#11671

brophdawg11 merged 5 commits intoremix-run:devremix-run/react-router:devfrom

nanianlisao:chore_createRouter_basenamenanianlisao/react-router:chore_createRouter_basenameCopy head branch name to clipboard